Patent Publication Number: US-2023137065-A1

Title: Gas sensor system, gas sensor calibration method, and gas sensor calibration program

Description:
The contents of the following Japanese patent application(s) are incorporated herein by reference: 
     NO. 2021-178213 filed in JP on Oct. 29, 2021 
     NO. 2022-171091 filed in JP on Oct. 26, 2022 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a gas sensor system, a gas sensor calibration method, and a gas sensor calibration program. 
     2. Related Art 
     Patent document 1 describes “an accurate carbon dioxide concentration measurement system is to be provided” (summary). 
     LIST OF CITED REFERENCES 
     Patent Document 
     
         
         Patent document 1: Japanese Patent Application Publication No. 2014-228518 
       
    
     The summary clause does not necessarily describe all necessary features of the embodiments of the present invention. The present invention may also be a sub-combination of the features described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example of calibration of gas concentrations in a first gas sensor apparatus  100  and a second gas sensor apparatus  200  according to an embodiment of the present invention. 
         FIG.  2    is a block diagram illustrating an example of a gas sensor system  400  according to an embodiment of the present invention. 
         FIG.  3    is a block diagram illustrating another example of the gas sensor system  400  according to an embodiment of the present invention. 
         FIG.  4    is a block diagram illustrating another example of the gas sensor system  400  according to an embodiment of the present invention. 
         FIG.  5    is a block diagram illustrating another example of the gas sensor system  400  according to an embodiment of the present invention. 
         FIG.  6    illustrates an example of calibration of gas concentrations in the first gas sensor apparatus  100 , the second gas sensor apparatus  200 , and a third gas sensor apparatus  300  according to an embodiment of the present invention. 
         FIG.  7    illustrates an example of calibration of gas concentrations in a gas sensor apparatus  150  and a gas sensor apparatus  250  according to an embodiment of the present invention. 
         FIG.  8    is a block diagram illustrating an example of the gas sensor apparatus  150  and the gas sensor apparatus  250  according to an embodiment of the present invention. 
         FIG.  9    is a block diagram illustrating another example of the gas sensor apparatus  150  and the gas sensor apparatus  250  according to an embodiment of the present invention. 
         FIG.  10    is a flowchart illustrating an example of a gas sensor calibration method according to an embodiment of the present invention. 
         FIG.  11    illustrates an example of a detail of calibration step S 104  in  FIG.  10   . 
         FIG.  12    is a flowchart illustrating another example of the gas sensor calibration method according to an embodiment of the present invention. 
         FIG.  13    is a flowchart illustrating an example of the gas sensor calibration method according to an embodiment of the present invention. 
         FIG.  14    is a flowchart illustrating an example of the gas sensor calibration method according to an embodiment of the present invention. 
         FIG.  15    illustrates an example of a detail of calibration step S 304  in  FIG.  14   . 
         FIG.  16    is a flowchart illustrating another example of the gas sensor calibration method according to an embodiment of the present invention. 
         FIG.  17    illustrates an example of a computer  2200  in which the gas sensor system  400 , the gas sensor apparatus  150 , or the gas sensor apparatus  250  according to an embodiment of the present invention may be entirely or partially embodied. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments are not intended to limit the invention according to claims. In addition, not all of the combinations of features described in the embodiments are essential to solving means of the invention. 
       FIG.  1    illustrates an example of calibration of gas concentrations in a first gas sensor apparatus  100  and a second gas sensor apparatus  200  according to an embodiment of the present invention. In the present example, a measurement target  501  is outdoor, and a measurement target  502  is indoor. 
     In the present example, a living body  90  has the first gas sensor apparatus  100 . The first gas sensor apparatus  100  may be a mobile terminal. The living body  90  is, for example, a person.  FIG.  1    illustrates a situation where the living body  90  having the first gas sensor apparatus  100  is moving from the measurement target  501  to the measurement target  502 . 
     A gas  503  is present in the measurement target  501 . The gas  503  may be CO 2  (carbon dioxide) gas, may be CH 4  (methane) gas, or may be alcohol. A gas sensor  600  configured to measure a concentration of the gas  503  in the measurement target  501  may be arranged in the measurement target  501 . When the measurement target  501  is outdoor, the gas sensor  600  measures the concentration of the gas  503  in outdoor air. The gas sensor  600  is, for example, an optical element. The gas sensor  600  may be a gas sensor based on non dispersive infrared (NDIR), may be a gas sensor based on optoacoustic spectroscopy, may be a gas sensor configured to detect a gas by a solid electrolyte, or may be a micro electro mechanical systems (MEMS) gas sensor. A detection method for the gas by the gas sensor  600  is not particularly limited. 
     A gas  504  is present in an interior space  508  in the measurement target  502 . The gas  504  may be CO 2  (carbon dioxide) gas, may be CH 4  (methane) gas, or may be alcohol. The interior space  508  may be a space isolated from the measurement target  501 . The interior space  508  may be a closed space. The interior space  508  is, for example, a room. 
     The second gas sensor apparatus  200  is arranged in the measurement target  502 . In the present example, the second gas sensor apparatus  200  is arranged in the interior space  508 . The second gas sensor apparatus  200  may be a mobile terminal. 
     A characteristic of the gas sensor  600  may change over a lapse of time. The characteristic of the gas sensor  600  refers to a characteristic of the optical element or the like when the gas sensor  600  is an optical element and is also a CO 2  (carbon dioxide) sensor configured to measure a gas concentration by infrared light. The characteristic of the optical element or the like may change over time. Thus, the gas sensor  600  is preferably calibrated. The gas sensor  600  is preferably regularly calibrated. 
     The gas sensor  600  may be subjected to self-calibration, or may be calibrated by another gas sensor  600 . The self-calibration refers to calibration of the gas sensor  600  itself based on a value of the gas concentration calculated by the gas sensor  600 . For the calibration of the gas sensor  600  itself, for example, a certain value of the gas concentration during a predetermined period, a maximum value or a minimum value of the gas concentration during the predetermined period, or the like may be used. For example, when the gas sensor  600  is a CO 2  (carbon dioxide) sensor, an output of the gas sensor  600  may be subjected to the self-calibration by an automatic baseline correction or automatic background calibration (ABC) algorithm. 
     When the measurement target  501  is outdoor and the gas sensor  600  is a CO 2  (carbon dioxide) sensor, the output of the gas sensor  600  may be calibrated at timing at which likelihood that a CO 2  (carbon dioxide) concentration in the air becomes a reference value of the CO 2  (carbon dioxide) concentration (for example, 400 ppm) is high. The output of the gas sensor  600  may be calibrated such that a CO 2  (carbon dioxide) concentration to be calculated based on the output of the gas sensor  600  indicates the reference value at the timing. The timing is, for example, a time slot in which an activity of the living body  90  is likely to be suppressed (for example, late at night). 
     The gas sensor  600  may transmit calibration information related to the calibration of the gas sensor  600 . The calibration information is set as calibration information Ic. The calibration information Ic is calibration information for calibrating the concentration of the gas  503  in the measurement target  501  which is calculated based on the output of the gas sensor  600 . The calibration information Ic is information related to calibration for causing the concentration of the gas  503  to approach a true value of the concentration. When the gas sensor  600  is a CO 2  (carbon dioxide) sensor, the calibration information Ic may be calibration information for calibrating the CO 2  (carbon dioxide) concentration such that the CO 2  (carbon dioxide) concentration to be calculated based on the output of the gas sensor  600  indicates the reference value at timing at which likelihood that a true value of the CO 2  (carbon dioxide) concentration becomes a reference value (for example, 400 ppm) is high. The gas sensor  600  may wirelessly transmit the calibration information Ic to an open space in the measurement target  501 . 
       FIG.  2    is a block diagram illustrating an example of a gas sensor system  400  according to an embodiment of the present invention. The gas sensor system  400  includes the first gas sensor apparatus  100  and the second gas sensor apparatus  200 . The first gas sensor apparatus  100  has a transmission unit  13 . The first gas sensor apparatus  100  may have a reception unit  10 , a control unit  15 , a calibration unit  14 , a display unit  12 , and an AD conversion unit  114 . 
     The control unit  15  is, for example, a central processing unit (CPU). The first gas sensor apparatus  100  may be a mobile terminal including the CPU. The mobile terminal may include a portable computer such as a smartphone or a tablet. The first gas sensor apparatus  100  may be a mobile terminal including the CPU, a memory, an interface, and the like. 
     The display unit  12  is, for example, a display, a monitor, or the like. When the first gas sensor apparatus  100  is a mobile terminal, the display unit  12  may be a display of the mobile terminal. 
     The first gas sensor apparatus  100  may have a first gas sensor  11 . When the first gas sensor apparatus  100  is arranged in the measurement target  501 , the first gas sensor  11  is configured to measure a concentration of the gas  503  in the measurement target  501 . The first gas sensor  11  may be a CO 2  (carbon dioxide) sensor, may be a CH 4  (methane) sensor, or may be an alcohol sensor. The first gas sensor  11  may measure the gas  503  (see  FIG.  1   ) of a same type as that for the gas sensor  600  (see  FIG.  1   ). That is, when the gas sensor  600  is a CO 2  (carbon dioxide) sensor, the first gas sensor  11  may be a CO 2  (carbon dioxide) sensor. 
     A characteristic of the first gas sensor  11  may change over a lapse of time. Thus, the first gas sensor  11  is preferably calibrated. In the present example, the reception unit  10  is configured to receive the calibration information Ic transmitted by the gas sensor  600 . In the present example, the calibration unit  14  is configured to calibrate, based on the calibration information Ic, the concentration of the gas  503  (see  FIG.  1   ) in the measurement target  501  (see  FIG.  1   ) which is calculated based on an output of the first gas sensor  11 . As a result, the measurement value of the concentration of the gas  503  by the first gas sensor  11  is more likely to be an accurate value than before the calibration. The calibration unit  14  may calibrate the concentration of the gas  503  (see  FIG.  1   ) in a state where the first gas sensor apparatus  100  is arranged in the measurement target  501  (in the present example, a state where the living body  90  is present outdoor). 
     The AD conversion unit  114  is configured to convert an output of an analog signal of the first gas sensor  11  into a digital signal. The calibration unit  14  may calibrate, based on the calibration information Ic, the concentration of the gas  503  (see  FIG.  1   ) which is calculated based on the output of the first gas sensor  11 . That is, after the concentration of the gas  503  is calculated, the calibration unit  14  may calibrate the calculated concentration of the gas  503 . While calculating the concentration of the gas  503 , the calibration unit  14  may calibrate the concentration of the gas  503  based on the output of the first gas sensor  11  and the calibration information Ic. 
     In the present example, the calibration unit  14  includes a computation unit  110  and a storage unit  112 . The computation unit  110  is configured to calculate the concentration of the gas  503  based on the digital signal of the first gas sensor  11  which is converted by the AD conversion unit  114 . The storage unit  112  is configured to store the concentration of the gas  503  which is calculated by the computation unit  110 . The storage unit  112  may store a correlation between the concentration of the gas  503  which is calculated by the computation unit  110  and the calibration information Ic. The correlation is set as a correlation Cr. The correlation Cr may be a correlation function or may be a correlation table. 
     The computation unit  110  may compute first calibration information Ic′ based on the calibration information Ic received by the reception unit  10  and the correlation Cr stored in the storage unit  112 . The first calibration information Ic′ is calibration information for calibrating the concentration of the gas  503  (see  FIG.  1   ) of the measurement target  501  (see  FIG.  1   ) which is calculated based on the output of the first gas sensor  11 . The first calibration information Ic′ is information related to calibration for causing the concentration of the gas  503  (see  FIG.  1   ) to approach a true value of the concentration. The calibration information Ic′ may be different from or may be identical to the calibration information Ic. 
     The computation unit  110  is, for example, a central processing unit (CPU). The computation unit  110  and the control unit  15  may be a single CPU. 
     The transmission unit  13  is configured to transmit the first calibration information Ic′ of the first gas sensor  11 . When the living body  90  (see  FIG.  1   ) remains in the measurement target  501  (see  FIG.  1   ), the transmission unit  13  may transmit the first calibration information Ic′ to the open space in the measurement target  501 . When the living body  90  has moved from the measurement target  501  to the measurement target  502  (see  FIG.  1   ), the transmission unit  13  may transmit the first calibration information Ic′ to the interior space  508 . The transmission unit  13  may wirelessly transmit the first calibration information Ic′. 
     Note that when the first gas sensor apparatus  100  does not have the first gas sensor  11 , a configuration may be adopted where the first gas sensor apparatus  100  does not have the AD conversion unit  114  too. When the first gas sensor apparatus  100  does not have the first gas sensor  11  and the AD conversion unit  114 , the output of the analog signal of the first gas sensor  11  may be converted into a digital signal by the AD conversion unit  114  arranged outside the first gas sensor apparatus  100 . The digital signal converted by the AD conversion unit  114  may be transmitted to the first gas sensor apparatus  100 . The same also applies when the second gas sensor apparatus  200  does not have a second gas sensor  21  (described below). 
     The second gas sensor apparatus  200  has a reception unit  20  and a calibration unit  24 . The second gas sensor apparatus  200  may have a control unit  25 , a display unit  22 , a transmission unit  23 , and an AD conversion unit  124 . Functions of the control unit  25 , the display unit  22 , and the transmission unit  23  may be respectively the same as those of the control unit  15 , the display unit  12 , and the transmission unit  13  in the first gas sensor apparatus  100 . 
     The reception unit  20  is configured to receive the first calibration information Ic′ transmitted by the transmission unit  13  of the first gas sensor apparatus  100 . The second gas sensor apparatus  200  may have the second gas sensor  21 . The calibration unit  24  is configured to calibrate, based on the first calibration information Ic′ received by the reception unit  20 , a concentration of the gas  504  (see  FIG.  1   ) of the measurement target  502  (see  FIG.  1   ) which is calculated based on an output of the second gas sensor  21 . As a result, a measurement value of the concentration of the gas  504  by the second gas sensor  21  is more likely to be an accurate value than before the calibration. 
     The AD conversion unit  124  is configured to convert an output of an analog signal of a second gas sensor  21  into a digital signal. The calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . That is, after the concentration of the gas  504  is calculated, the calibration unit  24  may calibrate the calculated concentration of the gas  504 . While calculating the concentration of the gas  504 , the calibration unit  24  may calibrate the concentration of the gas  504  based on the output of the second gas sensor  21  and the first calibration information Ic′. 
     As described above, the first calibration information Ic′ is the calibration information for calibrating the concentration of the gas  503  (see  FIG.  1   ) in the measurement target  501  (see  FIG.  1   ) which is calculated based on the output of the first gas sensor  11 . When the calibration unit  14  calibrates the concentration of the gas  503  (see  FIG.  1   ) in a state where the first gas sensor apparatus  100  is arranged in the measurement target  501  (in the present example, a state where the living body  90  is present outdoor) and also the first gas sensor apparatus  100  has moved from the measurement target  501  to the measurement target  502 , likelihood that the first gas sensor  11  can accurately measure the concentration of the gas  504  in the measurement target  502  is high. Thus, based on the first calibration information Ic′, the calibration unit  24  of the second gas sensor apparatus  200  is likely to accurately calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21 . 
     The gas sensor system  400  may include a storage unit  122 . In the present example, the second gas sensor apparatus  200  includes the storage unit  122 . In the present example, the calibration unit  24  includes a computation unit  120  and the storage unit  122 . Functions of the computation unit  120  and the storage unit  122  may be respectively the same as those of the computation unit  110  and the storage unit  112  in the calibration unit  14  of the first gas sensor apparatus  100 . 
     The storage unit  122  may store a correlation between the concentration of the gas  504  which is calculated by the computation unit  120  and the first calibration information Ic′. The correlation is set as a correlation Cr′. The computation unit  120  may compute second calibration information Ic″ based on the first calibration information Ic′ received by the reception unit  20  and the correlation Cr′ stored in the storage unit  122 . 
     The second calibration information Ic″ is calibration information for calibrating the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . The second calibration information Ic″ is information related to calibration for causing the concentration of the gas  504  (see  FIG.  1   ) to approach a true value of the concentration. The second calibration information Ic″ may be different from or may be identical to the first calibration information Ic′. 
     In the gas sensor system  400 , the reception unit  20  is configured to receive the first calibration information Ic′, and also the calibration unit  24  is configured to calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . As a result, the gas sensor system  400  can calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21 . 
     When the interior space  508  (see  FIG.  1   ) is a closed space isolated from outdoor, a case is conceivable that the CO 2  (carbon dioxide) concentration in the interior space  508  does not become the above described reference value (for example, 400 ppm) even in a time slot in which the activity of the living body  90  is likely to be suppressed (for example, late at night). When the CO 2  (carbon dioxide) concentration in the interior space  508  does not become the reference value, it is difficult for the second gas sensor  21  to perform the self-calibration of the measured concentration of the gas  504  (see  FIG.  1   ). 
     In the present example, in a state where the first gas sensor apparatus  100  is arranged in the measurement target  501  (in the present example, a state where the living body  90  is present outdoor), the concentration of the gas  503  (see  FIG.  1   ) which is calculated based on the output of the first gas sensor  11  is calibrated by the calibration unit  14 . Thus, when the living body  90  has moved from the measurement target  501  (see  FIG.  1   ) to the interior space  508  (see  FIG.  1   ), the first gas sensor apparatus  100  is likely to accurately measure the concentration of the gas  504  in the interior space  508 . 
     In the present example, after the living body  90  has moved to the interior space  508 , the transmission unit  13  transmits the first calibration information Ic′. Thus, even when the second gas sensor apparatus  200  is arranged in an environment (in the present example, the interior space  508 ) where it is difficult to perform the self-calibration, the gas sensor system  400  can calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21 . The gas sensor system  400  can calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  in a state where the second gas sensor apparatus  200  is arranged in the measurement target  502  (see  FIG.  1   ). 
     The calibration information Ic may be a reading of the concentration of the gas  503  (see  FIG.  1   ) in the measurement target  501  (see  FIG.  1   ). The reading of the concentration of the gas  503  may be a concentration of the gas  503  which is calculated based on the output of the gas sensor  600  (see  FIG.  1   ). 
     A predetermined distance between the gas sensor  600  and the first gas sensor  11  is set as a distance dp 1 . When the distance between the gas sensor  600  and the first gas sensor  11  is less than the distance dp 1 , likelihood that the gas sensor  600  and the first gas sensor  11  are arranged in the measurement target  501  with the same concentration of the gas  503  is high. Thus, the concentration of the gas  503  which is calculated based on the output of the gas sensor  600  and the concentration of the gas  503  which is calculated based on the output of the first gas sensor  11  are preferably identical. Thus, when the distance between the gas sensor  600  and the first gas sensor  11  is less than the distance dp 1 , the calibration information Ic may be a reading of the concentration of the gas  503  in the measurement target  501 . The distance dp 1  is, for example, 10 m. When the gas sensor  600  and the first gas sensor  11  are arranged in the interior space  508 , the distance dp 1  may be 5 m. 
     The calibration information Ic may be a calibration amount of the concentration of the gas  503  (see  FIG.  1   ) in the measurement target  501  (see  FIG.  1   ). The concentration of the gas  503  which is calculated based on the output of the gas sensor  600  (see  FIG.  1   ) is set as a concentration C 0 . The concentration of the gas  503  which is calculated based on the output of the first gas sensor  11  is set as a concentration C 1 . The calibration amount of the concentration of the gas  503  may be a difference between the concentration C 0  and the concentration C 1 . 
     When the calibration amount of the concentration of the gas  503  is a difference between the concentration C 0  and the concentration C 1 , the calibration unit  14  may calibrate, by the difference, the output of the gas  503  by the first gas sensor  11 . The calibration unit  14  may offset the output of the gas  503  by the first gas sensor  11  by the difference. 
     When it is assumed that a state of the gas sensor  600  is comparable to a state of the first gas sensor  11 , the calibration information Ic is preferably a calibration amount of the concentration of the gas  503  (see  FIG.  1   ). A situation where the state of the gas sensor  600  is comparable to the state of the first gas sensor  11  is, for example, a case where likelihood that a deterioration state of the gas sensor  600  is comparable to a deterioration state of the first gas sensor  11  is high. A case where the likelihood that the deterioration state of the gas sensor  600  is comparable to the deterioration state of the first gas sensor  11  is high may be a case where at least one of a case where a most recent calibration period of the gas sensor  600  is the same as a most recent calibration period of the first gas sensor  11 , a case where an environment in which the gas sensor  600  is arranged is similar to an environment in which the first gas sensor  11  is arranged, or a case where a specification of the gas sensor  600  is the same as a specification of the first gas sensor  11  is satisfied. The environment in which the gas sensor  600  is arranged may refer to at least one of a temperature, a humidity, or a concentration of the gas  503  in a location where the gas sensor  600  is arranged. 
     The first calibration information Ic′ may be a reading of the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  (see  FIG.  1   ). The reading of the concentration of the gas  504  may be a concentration of the gas  504  which is calculated based on the output of the first gas sensor  11 . 
     A predetermined distance between the first gas sensor  11  and the second gas sensor  21  is set as a distance dp 2 . Similarly as in the case of the calibration information Ic, when the distance between the first gas sensor  11  and the second gas sensor  21  is less than the distance dp 2 , the first calibration information Ic′ may be a reading of the concentration of the gas  504  in the measurement target  502 . 
     Similarly as in the case of the calibration information Ic, the first calibration information Ic′ may be a calibration amount of the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  (see  FIG.  1   ). When it is assumed that the state of the first gas sensor  11  is comparable to the state of the second gas sensor  21 , the first calibration information Ic′ is preferably the calibration amount of the concentration of the gas  504  due to a reason similar to the above described reason with regard to the case of the calibration information Ic. 
     A concentration of the gas  504  (see  FIG.  1   ) which is calculate based on the output of the first gas sensor  11  is set as a concentration C 1 ′. A concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  is set as a concentration C 2 . When the calibration amount of the concentration of the gas  504  is a difference between the concentration C 1 ′ and the concentration C 2 , the calibration unit  24  may calibrate, by the difference, the concentration C 2  calculated based on the output of the second gas sensor  21 . 
     The transmission unit  23  of the second gas sensor apparatus  200  may transmit the concentration C 2  to the first gas sensor apparatus  100 . In  FIG.  2   , a path in which the concentration C 2  is to be transmitted to the first gas sensor apparatus  100  is represented by a coarse dotted arrow. When the transmission unit  23  transmits the concentration C 2  to the first gas sensor apparatus  100 , the concentration C 2  may be a concentration of the gas  504  before being calibrated by the calibration unit  24 . The reception unit  10  of the first gas sensor apparatus  100  may receive the concentration C 2 . The computation unit  110  of the first gas sensor apparatus  100  may compute a difference between the concentration C 1 ′ and the concentration C 2 . The transmission unit  13  may transmit the difference to the reception unit  20 . The calibration unit  24  may calibrate, by the difference, the concentration C 2  received by the reception unit  20 . 
     The first gas sensor apparatus  100  may be subjected to self-calibration. When the first gas sensor  11  is a CO 2  (carbon dioxide) sensor, the first gas sensor apparatus  100  may be subjected to the self-calibration by an automatic baseline correction or automatic background calibration (ABC) algorithm. When the measurement target  501  (see  FIG.  1   ) is an environment in which the self-calibration can be performed (for example, outdoor) and the first gas sensor apparatus  100  is arranged in the measurement target  501 , the first gas sensor apparatus  100  may be subjected to the self-calibration in a state of being arranged in the measurement target  501 . The concentration C 2  to be calculated based on the output of the second gas sensor  21  may be calibrated based on the first calibration information Ic′ of the first gas sensor  11  on which the self-calibration has been performed. 
     The first gas sensor apparatus  100  may or may not include the first gas sensor  11 . In the present example, the first gas sensor apparatus  100  includes the first gas sensor  11 . When the first gas sensor apparatus  100  does not include the first gas sensor  11 , the output of the first gas sensor  11  may be transmitted to the calibration unit  14 . The same also applies to the second gas sensor apparatus  200 . 
     In the present example, the measurement target  502  in which the concentration C 1 ′ is calculated based on the output of the first gas sensor  11  is the same as the measurement target  502  in which the concentration C 2  is calculated based on the output of the second gas sensor  21 . A situation where the measurement target  502  in which the concentration C 1 ′ is calculated is the same as the measurement target  502  in which the concentration C 2  is calculated may refer to a situation where a type of a measurement target gas of the first gas sensor apparatus  100  is the same as a type of a measurement target gas of the second gas sensor apparatus  200  in the measurement target  502 . The measurement target gas of the first gas sensor apparatus  100  and the second gas sensor apparatus  200  may be CO 2  (carbon dioxide), may be CH 4  (methane), or may be alcohol. 
     A situation where the measurement target  502  in which the concentration C 1 ′ is calculated is the same as the measurement target  502  in which the concentration C 2  is calculated may refer to a situation where the first gas sensor  11  and the second gas sensor  21  share a same space (in the present example, the interior space  508  (see  FIG.  1   )). The same space may refer to at least one of a case where a temperature or a humidity in the space is the same, a case where an ID of short distance radio (Wi-Fi (registered trademark) or the like) is the same, or a case where, when the first gas sensor apparatus  100  and the second gas sensor apparatus  200  are a mobile terminal, an amplitude and a frequency of acoustic waves acquired by the mobile terminal are the same. 
     Note that in the measurement target  502 , a type of the measurement target gas the concentration C 1 ′ of which is calculated based on the output of the first gas sensor  11  may be different from a type of the measurement target gas the concentration C 2  of which is calculated based on the output of the second gas sensor  21 . The type of the measurement target gas the concentration C 1 ′ of which is calculated based on the output of the first gas sensor  11  is set as a gas type G 1 . The type of the measurement target gas the concentration C 2  of which is calculated based on the output of the second gas sensor  21  is set as a gas type G 2 . When the gas type G 1  is different from the gas type G 2 , the first calibration information Ic′ may include information of the gas type G 1 . The calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas of the gas type G 2  which is calculated based on the output of the second gas sensor. 
     Note that when the first gas sensor  11  is arranged in the measurement target  501  and the second gas sensor  21  is arranged in the measurement target  502 , likelihood that the concentration of the gas  503  in the measurement target  501  is different from the concentration of the gas  504  in the measurement target  502  is high. Thus, when the first gas sensor  11  is arranged in the measurement target  501  and the second gas sensor  21  is arranged in the measurement target  502 , a configuration may be adopted where the calibration unit  24  does not calibrate the concentration C 2  which is calculated based on the output of the second gas sensor  21 . 
       FIG.  3    is a block diagram illustrating another example of the gas sensor system  400  according to an embodiment of the present invention. A calibration reliability of the first gas sensor apparatus  100  is set as a calibration reliability R 1 . Reliability information indicating the calibration reliability R 1  is set as reliability information Ir 1 . The reliability information Ir 1  is information indicating, when the first gas sensor apparatus  100  is calibrated, a reliability of the calibration performed on the first gas sensor apparatus  100 . The reliability information Ir 1  may include at least one of information on an elapsed period of time from the most recent calibration, information on an elapsed period of time since the first gas sensor  11  is installed, information on calibration means, information related to a diversity of a calibration source, information on the number of times to perform calibration, information on a calibration frequency, information of a gas concentration at the time of calibration, or environment information at the time of calibration. 
     The calibration reliability R 1  is more likely to be higher as the elapsed period of time from the most recent calibration is shorter. The reliability information Ir 1  may be stored in the storage unit  112 . 
     The information of the calibration means is information indicating whether the first gas sensor apparatus  100  is subjected to the self-calibration or is calibrated by another sensor (for example, the gas sensor  600  (see  FIG.  1   )). When the first gas sensor apparatus  100  is calibrated by another sensor, the information of the calibration means may include at least one of a distance between the first gas sensor and the other sensor or a calibration state of the other sensor. Note that in the first gas sensor apparatus  100 , by calibrating the output of the first gas sensor  11  by the calibration unit  14 , the self-calibration on the first gas sensor  11  may be performed. 
     The information related to the diversity of the calibration source may include at least one of: a number of at least one sensor (for example, the gas sensor  600  (see  FIG.  1   )) as the calibration source of the first gas sensor  11 ; or a number of at least one specification of the sensor as the calibration source. The specification of the sensor is, for example, a specific configuration of the sensor. When the first gas sensor apparatus  100  is subjected to the self-calibration, the number of sensors of the calibration source and the number of specifications of the sensor of the calibration source may include the first gas sensor  11 . As the number of sensors of the calibration source is higher, the calibration reliability R 1  is more likely to be increased. As the number of specifications of the sensor of the calibration source is higher, the calibration reliability R 1  is more likely to be increased. 
     The information of the number of times to perform calibration is information related to the number of times the first gas sensor apparatus  100  has been calibrated from a predetermined time point in the past to the present. The number of times to perform calibration may include a case where the first gas sensor apparatus  100  has been subjected to the self-calibration and a case where the first gas sensor apparatus  100  has been calibrated by another sensor. As the number of times to perform calibration is higher, the calibration reliability R 1  is more likely to be increased. 
     The information of the calibration frequency is information of the number of times to perform calibration on the first gas sensor apparatus  100  per predetermined period of time. The number of times to perform calibration may include a case where the first gas sensor apparatus  100  has been subjected to the self-calibration and a case where the first gas sensor apparatus  100  has been calibrated by another sensor. As the calibration frequency is higher, the calibration reliability R 1  is more likely to be increased. 
     Information of the gas concentration at the time of calibration is information of a gas concentration at the time of calibration of the first gas sensor apparatus  100 . The time of calibration of the first gas sensor apparatus  100  may include the time of the self-calibration of the first gas sensor apparatus  100  and the time of the calibration of the first gas sensor apparatus  100  by another sensor. When the first gas sensor apparatus  100  is calibrated at the time of measurement of a gas concentration that is not within a predetermined range (for example, an abnormal value of the gas concentration), the calibration reliability R 1  is more likely to be decreased as compared with a case the calibration is performed at the time of measurement of a gas concentration at a reference value. 
     The environment information at the time of calibration may include a temperature, a humidity, or an air pressure of a space (for example, the measurement target  501  (see  FIG.  1   )) in which the first gas sensor  11  is arranged at the time of calibration of the first gas sensor apparatus  100 . When the first gas sensor  11  is calibrated at a temperature that is not in a predetermined range (for example, an abnormal value of the temperature), a humidity that is not in a predetermined range (for example, an abnormal value of the humidity), or an air pressure that is not in a predetermined range (for example, an abnormal value of the air pressure), the calibration reliability R 1  is more likely to be decreased as compared with a case where the calibration is performed at a temperature at a reference value, a humidity at a reference value, or an air pressure at a reference value. 
     The transmission unit  13  may further transmit the reliability information Ir 1 . The reception unit  20  of the second gas sensor apparatus  200  may further receive the reliability information Ir 1 . The calibration unit  24  may calibrate, based on the first calibration information Ic′ and the calibration reliability R 1  of the first gas sensor apparatus  100 , the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . The calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21  according to the reliability information Ir 1 . 
     A calibration reliability of the second gas sensor apparatus  200  is set as a calibration reliability R 2 . Reliability information indicating the calibration reliability R 2  is set as reliability information Ir 2 . The reliability information Ir 2  is information indicating, when the second gas sensor apparatus  200  is calibrated, a reliability of the calibration performed on the second gas sensor apparatus  200 . The reliability information Ir 2  may include information similar to the reliability information Ir 1  described above. The reliability information Ir 2  and the reliability information Ir 1  which has been received by the reception unit  20  may be stored in the storage unit  122 . 
     A predetermined threshold of the calibration reliability R 1  is set as a first threshold Rth 1 . The first threshold Rth 1  may be different for each of the measurement targets  501  (see  FIG.  1   ). When the calibration reliability R 1  exceeds the first threshold Rth 1 , a user of the gas sensor system  400  may trust the concentration of the gas  503  (see  FIG.  1   ) which is calculated based on the output of the first gas sensor  11 . 
     A predetermined threshold of the calibration reliability R 2  is set as a second threshold Rth 2 . The second threshold Rth 2  may be different for each of the measurement targets  502  (see  FIG.  1   ). When the calibration reliability R 2  exceeds the second threshold Rth 2 , the user of the gas sensor system  400  may trust the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . Note that the second threshold Rth 2  and the first threshold Rth 1  may be the same or may be different from each other. 
     The reliability information Ir 2  may include information of a reliability of self-calibration in the second gas sensor apparatus  200 . The self-calibration refers to calibration that is not based on another gas sensor (in the present example, for example, the first gas sensor apparatus  100 ). When the second gas sensor  21  is a CO 2  (carbon dioxide) sensor, the self-calibration may refer to calibration based on an automatic baseline correction or automatic background calibration (ABC) algorithm. 
     The information of the reliability of the self-calibration in the second gas sensor apparatus  200  may include information on whether the second gas sensor apparatus  200  has a function of the self-calibration. The second gas sensor apparatus  200  may perform the self-calibration of the second gas sensor apparatus  200  by calibrating the output of the second gas sensor  21  by the calibration unit  24 . 
     When the calibration reliability R 1  is equal to or lower than the first threshold Rth 1 , a configuration may be adopted where the calibration unit  24  does not calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . When the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  is equal to or lower than the second threshold Rth 2  and also the calibration reliability R 1  exceeds the first threshold Rth 1 , the calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . A case where the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  is equal to or lower than the second threshold Rth 2  may include a case where the second gas sensor apparatus  200  does not have a function of the self-calibration. A case where the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  is equal to or lower than the second threshold Rth 2  may include a case where the self-calibration is difficult due to a reason that the second gas sensor apparatus  200  is an old sensor device, or the like. 
     The calibration unit  24  may compare the calibration reliability R 1  of the first gas sensor apparatus  100  which his received by the reception unit  20  with the calibration reliability R 2  of the second gas sensor apparatus  200 . The calibration reliability R 2  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  and the calibration reliability R 2  in a case where the second gas sensor apparatus  200  is calibrated by another sensor. 
     When the calibration reliability R 1  of the first gas sensor apparatus  100  is higher than the calibration reliability R 2  of the second gas sensor apparatus  200 , the calibration unit  24  may calibrate, based on the first calibration information Ic′ received by the reception unit  20 , the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . Since the concentration of the gas  504  is calibrated, the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  is likely to be accurate. When the calibration reliability R 1  is equal to or lower than the calibration reliability R 2 , a configuration may be adopted where the calibration unit  24  does not calibrate the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21  but may perform calibration based on the second calibration information Ic″. 
     When the calibration reliability R 2  is equal to or lower than the second threshold Rth 2 , the transmission unit  23  of the second gas sensor apparatus  200  may transmit information to another gas sensor apparatus (for example, at least one of the gas sensor  600  or the first gas sensor apparatus  100 ) for requesting transmission of calibration information for calibrating the output of the second gas sensor  21  to the second gas sensor apparatus  200 . When the calibration reliability R 2  is equal to or lower than the second threshold Rth 2 , the second gas sensor apparatus  200  may be in a standby state. As a result, power consumption of the second gas sensor apparatus  200  is likely to be reduced. 
     The calibration reliability R 1  of the first gas sensor apparatus  100  which is received by the reception unit  20  may be stored in the storage unit  122 . The calibration reliability R 1  stored in the storage unit  122  may refer to the past calibration reliability R 1  the first gas sensor apparatus  100 . The calibration unit  24  may compare the calibration reliability R 1  stored in the storage unit  122  with the current calibration reliability R 1  of the first gas sensor apparatus  100  which is received by the reception unit  20 . When the current calibration reliability R 1  of the first gas sensor apparatus  100  is higher than the calibration reliability R 1  of the first gas sensor apparatus  100  which is stored in the storage unit  122 , the calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . 
     A calibration reliability serving as a reference for calibrating the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  is set as a reference calibration reliability Cs. Reference reliability information indicating the reference calibration reliability Cs is set as reference reliability information Irs. The reference calibration reliability Cs may be at least one of the calibration reliability R 1  of the first gas sensor apparatus  100  or the calibration reliability R 2  of the second gas sensor apparatus  200 . When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received by the reception unit  20  is higher than the reference calibration reliability Cs, the calibration unit  24  may calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . 
     The storage unit  122  may store the reference reliability information Cs. When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received by the reception unit  20  is higher than the reference calibration reliability Cs, the storage unit  122  may update the reference calibration reliability Cs based on the received calibration reliability R 1  and store the updated reference calibration reliability Cs. The calibration unit  24  may calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21  according to the updated reference reliability Cs. 
     When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received by the reception unit  20  is higher than the reference calibration reliability Cs, the storage unit  122  may update the reference calibration reliability Cs to the calibration reliability R 1  and store the updated reference calibration reliability Cs. When the calibration reliability R 1  is lower than the reference calibration reliability Cs, a configuration may be adopted where the storage unit  122  does not update the reference calibration reliability Cs. 
     The reference reliability information Cs stored in the storage unit  122  may be the reference reliability information Cs updated based on the calibration reliability R 1  or may be the calibration reliability R 2 . The calibration reliability R 2  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  and the calibration reliability R 2  in a case where the second gas sensor apparatus  200  is calibrated by another sensor. 
       FIG.  4    is a block diagram illustrating another example of the gas sensor system  400  according to an embodiment of the present invention. In the gas sensor system  400  of the present example, the first gas sensor apparatus  100  further has a position information acquisition unit  16 , and the second gas sensor apparatus  200  further has a position information acquisition unit  26 . The gas sensor system  400  of the present example is different from the example illustrated in  FIG.  3    in the above described aspect. 
     The position information acquisition unit  16  is configured to acquire information of a position of the first gas sensor apparatus  100 . The position information acquisition unit  26  is configured to acquire information of a position of the second gas sensor apparatus  200 . The position information acquisition unit  16  and the position information acquisition unit  26  are, for example, a global positioning system (GPS). 
     The position information of the first gas sensor apparatus  100  is set as position information Ip 1 . The reliability information Ir 1  may include the position information Ip 1 . The position information of the second gas sensor apparatus  200  is set as position information Ip 2 . The reliability information Ir 2  may include the position information Ip 2 . 
     A distance between the position of the first gas sensor apparatus  100  and the position of the second gas sensor apparatus  200  which is acquired by the position information acquisition unit  26  is set as a distance d. As described above, the predetermined distance between the position of the first gas sensor  11  and the position of the second gas sensor  21  is the distance dp 2 . The distance dp 2  may refer to a distance at which likelihood that the first gas sensor  11  and the second gas sensor  21  are arranged in a same space (for example, the interior space  508  of  FIG.  1   ) is high. The same space may refer to a situation where a type of the measurement target gas the concentration C 1 ′ of which is calculated based on the output of the first gas sensor  11  is the same as a type of the measurement target gas the concentration C 2  of which is calculated based on the output of the second gas sensor  21 , or may refer to a situation where an ID of short distance radio (Wi-Fi (registered trademark) or the like) in the space where the first gas sensor  11  is arranged is the same as an ID of short distance radio (Wi-Fi (registered trademark) or the like) in the space where the second gas sensor  21  is arranged. 
     The calibration unit  24  may calibrate, based on the distance d and the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . When the distance d is less than the distance dp 2 , the calibration unit  24  may calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21 . When the distance d is equal to or more than the distance dp 2 , a configuration may be adopted where the calibration unit  24  does not calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21 . The calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21  according to the distance d. 
     Note that the reliability information Ir 1  may include information of a user of the first gas sensor apparatus  100 . The information of the user may include a plurality of usernames and a past use history of the first gas sensor apparatus  100  for each of the usernames. The past use history may include a past use situation. The past use situation is, for example, a situation where a particular user intentionally blows exhalation to the first gas sensor apparatus  100 , or the like. The calibration reliability R 1  in a case where the first gas sensor apparatus  100  is used by the particular user may be lower than the calibration reliability R 1  in a case where the first gas sensor apparatus  100  is used by another user. The particular user may be stored as a person on watch list in the storage unit  122 . 
       FIG.  5    is a block diagram illustrating another example of the gas sensor system  400  according to an embodiment of the present invention. The gas sensor system  400  of the present example is different from the gas sensor system  400  illustrated in  FIG.  2    in that a plurality of first gas sensor apparatuses  100  (a first gas sensor apparatus  100 - 1  to a first gas sensor apparatus  100 - n ) are included. In  FIG.  5   , an illustration of the gas  503  in the measurement target  501  and the gas  504  in the measurement target  502  is omitted. 
     Each of the first gas sensor apparatus  100 - 1  to the first gas sensor apparatus  100 - n  may be possessed by each of a plurality of living bodies  90  (a living body  90 - 1  to a living body  90 - n ). The plurality of first gas sensor apparatuses  100  may be moved from the measurement target  501  to the measurement target  502  when the plurality of living bodies  90  move from the measurement target  501  to the measurement target  502 . 
     In the present example, the first gas sensor apparatus  100 - 1  to the first gas sensor apparatus  100 - n  respectively have a reception unit  10 - 1  to a reception unit  10 - n , respectively have a calibration unit  14 - 1  to a calibration unit  14 - n , and respectively have a transmission unit  13 - 1  to a transmission unit  13 - n . In the present example, the first gas sensor apparatus  100 - 1  to the first gas sensor apparatus  100 - n  respectively have a first gas sensor  11 - 1  to a first gas sensor  11 - n . In  FIG.  5   , an internal configuration of the first gas sensor apparatus  100  is omitted. 
     A plurality of gas sensors  600  (a gas sensor  600 - 1  to a gas sensor  600 - n ) may be arranged in the measurement target  501 . The gas sensor  600 - 1  to the gas sensor  600 - n  may respectively transmit calibration information Ic 1  to calibration information Icn. The calibration information Ic 1  to the calibration information Icn may be different from each other, or may be the same. 
     The calibration unit  14 - 1  may calibrate, based on the calibration information Ic 1  to the calibration information Icn, the concentration of the gas  503  (see  FIG.  1   ) of the measurement target  501  which is calculated based on the output of the first gas sensor  11 - 1 . The calibration unit  14 - 2  may calibrate, based on the calibration information Ic 1  to the calibration information Icn, the concentration of the gas  503  in the measurement target  501  which is calculated based on the output of the first gas sensor  11 - 2 . Similarly, the calibration unit  14 - n  may calibrate, based on the calibration information Ic 1  to the calibration information Icn, the concentration of the gas  503  in the measurement target  501  which is calculated based on the output of the first gas sensor  11 - n.    
     In the present example, the calibration unit  14  of one first gas sensor apparatus  100  is configured to calibrate, based on the plurality of pieces of calibration information Ic, the concentration of the gas  503  (see  FIG.  1   ) which is calculated based on the output of the first gas sensor  11  of the one first gas sensor apparatus  100 . Thus, the output of the first gas sensor  11  is more likely to be calibrated to an accurate concentration as compared with a case where the output of the first gas sensor  11  is calibrated based on one piece of the calibration information Ic. 
     In the present example, the calibration unit  14 - 1  to the calibration unit  14 - n  respectively include a computation unit  120 - 1  to a computation unit  120 - n . The computation unit  120 - 1  to the computation unit  120 - n  may respectively compute first calibration information Ic′ 1  to first calibration information Ic′n. The gas concentration calculated based on the outputs of the first gas sensor  11 - 1  to the first gas sensor  11 - n  may be respectively calibrated based on the first calibration information Ic′ 1  to the first calibration information Ic′n. 
     The transmission unit  13 - 1  to the transmission unit  13 - n  may respectively transmit the first calibration information Ic′ 1  to the first calibration information Ic′n. When the plurality of living bodies  90  (see  FIG.  1   ) have moved to the measurement target  502 , the transmission unit  13 - 1  to the transmission unit  13 - n  may respectively transmit the first calibration information Ic′ 1  to the first calibration information Ic′n to the interior space  508 . 
     The reception unit  20  of the second gas sensor apparatus  200  may receive the first calibration information Ic′ in each of the plurality of first gas sensor apparatuses  100 . In the present example, the reception unit  20  receives the first calibration information Ic′ 1  to the first calibration information Ic′n respectively transmitted by the transmission unit  13 - 1  to the transmission unit  13 - n.    
     The calibration unit  24  of the second gas sensor apparatus  200  may calibrate, based on the plurality of first calibration information Ic′, the concentration the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . In the present example, the calibration unit  24  calibrates the concentration of the gas  504  based on the first calibration information Ic′ 1  to the first calibration information Ic′n. As a result, the output of the second gas sensor  21  is more likely to be calibrated to an accurate concentration as compared with a case where the output of the second gas sensor  21  is calibrated based on one piece of the first calibration information Ic′. 
     Reliability information indicating the calibration reliabilities of the first gas sensor  11 - 1  to the first gas sensor  11 - n  are respectively set as a calibration reliability R 11  to a calibration reliability R 1   n . Reliability information indicating the calibration reliability R 11  to the calibration reliability R 1   n  are respectively set as reliability information Ir 1 - 1  to reliability information Ir 1 - n . The transmission unit  13  (see  FIG.  2    to  FIG.  4   ) of each of the plurality of first gas sensor apparatuses  100  may transmit the reliability information Ir 1  of each of the first gas sensor apparatuses  100 . In the present example, the transmission unit  13 - 1  to the transmission unit  13 - n  respectively transmit the reliability information Ir 1 - 1  to the reliability information Ir 1 - n.    
     The reception unit  20  of the second gas sensor apparatus  200  may receive the reliability information Ir 1 - 1  to the reliability information Ir 1 - n . The calibration unit  24  may apply a weighting to the calibration reliability R 11  to the calibration reliability R 1   n . The application of the weighting to the calibration reliability R 11  to the calibration reliability R 1   n  refers to a configuration where a weighting to the calibration reliability R 1  with a high reliability is set to be greater than a weighting to the calibration reliability R 1  with a low reliability. The calibration unit  24  may calibrate, based on the calibration reliability R 1  to which the weighting has been applied, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . 
     The reliability information Ir 1 - 1  to the reliability information Ir 1 - n  may be stored in the storage unit  122 . The computation unit  120  may compute a weighting of the calibration reliability R 11  to the calibration reliability R 1   n  based on the reliability information Ir 1 - 1  to the reliability information Ir 1 - n  which are stored in the storage unit  122 . The computation unit  120  may compute the second calibration information Ic″ by applying the weighting to the calibration reliability R 11  to the calibration reliability R 1   n . The calibration unit  24  may calibrate, based on the second calibration information Ic″, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . As a result, the concentration of the gas  504  is more likely to be calibrated to an accurate concentration as compared with a case where the concentration of the gas  504  is calibrated based on the second calibration information Ic″ to which no weighting of the calibration reliability R 11  to the calibration reliability R 1   n  has been applied. 
     When the reliability information Ir 1  in which the calibration reliability R 1  of the first gas sensor apparatus  100  is lower than the first threshold Rth 1  is included in any of the reliability information Ir 1 - 1  to the reliability information Ir 1 - n , the computation unit  120  may compute a weighting by eliminating the calibration reliability R 1  that is lower than the first threshold Rth 1 . The computation by the computation unit  120  on a weighting by eliminating the calibration reliability R 1  may refer to computation by the computation unit  120  to set a weighting of the calibration reliability R 1  as zero. 
     The calibration unit  24  may calibrate, based on the highest calibration reliability R 1  among the calibration reliability R 11  to the calibration reliability R 1   n , the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . The calibration unit  24  may calibrate the concentration of the gas  504  by setting a weighting of the highest calibration reliability R 1  as  1  and setting a weighting of the other calibration reliabilities R 1  as zero. 
       FIG.  6    illustrates an example of calibration of the gas concentration in the first gas sensor apparatus  100 , the second gas sensor apparatus  200 , and a third gas sensor apparatus  300  according to an embodiment of the present invention. The third gas sensor apparatus  300  may have a reception unit  30 , a third gas sensor  31 , a display unit  32 , a transmission unit  33 , a calibration unit  34 , and a control unit  35 . The block diagram of the third gas sensor apparatus  300  may be the same as the block diagrams of the first gas sensor apparatus  100  and the second gas sensor apparatus  200  which are illustrated in  FIG.  2    to  FIG.  4   . 
     In the present example, the first gas sensor apparatus  100  moves from the measurement target  501  to a measurement target  505 . The measurement target  505  may be outdoor, or may be indoor. When the measurement target  505  is outdoor, the gas concentration in the measurement target gas which is calculated based on the output of the first gas sensor  11  in the measurement target  501  and the gas concentration in the measurement target gas which is calculated based on the output of the first gas sensor  11  in the measurement target  505  may be the same or may be different from each other. 
     In the present example, the transmission unit  23  of the first gas sensor apparatus  100  in the measurement target  505  is configured to transmit first calibration information Icm. The transmission units  23  of the first gas sensor apparatus  100 - 1  to the first gas sensor apparatus  100 - n  may respectively transmit first calibration information Icm 1  to first calibration information Icmn. In the present example, the reception unit  30  of the third gas sensor apparatus  300  is configured to receive the first calibration information Icm in the measurement target  505 . The reception units  30  of the third gas sensor apparatus  300 - 1  to the third gas sensor apparatus  300 - n  may respectively receive the first calibration information Icm 1  to the first calibration information Icmn. 
     In the present example, the calibration unit  34  of the third gas sensor apparatus  300  is configured to calibrate, based on the first calibration information Icm received by the reception unit  30 , a concentration of a gas in the measurement target  505  which is calculated based on the output of the third gas sensor  31 . The calibration units  34  of the third gas sensor apparatus  300 - 1  to the third gas sensor apparatus  300 - n  may respectively calibrate, based on the first calibration information Icm 1  to the first calibration information Icmn, the concentration of the gas in the measurement target  505  which is calculated based on outputs of the respective third gas sensors  31  of the third gas sensor apparatus  300 - 1  to the third gas sensor apparatus  300 - n.    
     In the present example, the third gas sensor apparatus  300  in which the concentration of the gas in the measurement target  505  has been calibrated moves from the measurement target  505  to the measurement target  502 . In the present example, the transmission unit  33  of the third gas sensor apparatus  300  is configured to transmit the calibration information Ic′ of the third gas sensor apparatus  300 . The transmission units  33  of the third gas sensor apparatus  300 - 1  to the third gas sensor apparatus  300 - n  may respectively transmit the calibration information Ic′ 1  to the calibration information Ic′n. In the present example, the reception unit  20  of the second gas sensor apparatus  200  is configured to receive the calibration information Ic′ in the measurement target  502 . The reception unit  20  of the second gas sensor apparatus  200  may receive the calibration information Ic′ 1  to the calibration information Ic′n. 
     In the present example, the calibration unit  24  of the second gas sensor apparatus  200  is configured to calibrate, based on the calibration information Ic′ received by the reception unit  20 , the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . In the present example, calibration information of a plurality of types (the calibration information Ic and the calibration information Icm) is to be reflected on the calibration information Ic′. Thus, the second gas sensor apparatus  200  is more likely to be accurately calibrated as compared with a case where calibration information of one type is to be reflected on the calibration information Ic′ (for example, the case of  FIG.  5   ). 
       FIG.  7    illustrates an example of calibration of gas concentrations of a gas sensor apparatus  150  and a gas sensor apparatus  250  according to an embodiment of the present invention. The gas sensor apparatus  150  may be the same as the first gas sensor apparatus  100  illustrated in  FIG.  1    to  FIG.  6   . The gas sensor apparatus  250  may be the same as the second gas sensor apparatus  200  illustrated in  FIG.  1    to  FIG.  6   . 
       FIG.  8    is a block diagram illustrating an example of the gas sensor apparatus  150  and the gas sensor apparatus  250  according to an embodiment of the present invention. The gas sensor apparatus  150  may be the same as the first gas sensor apparatus  100  illustrated in  FIG.  4   . The gas sensor apparatus  250  may be the same as the second gas sensor apparatus  200  illustrated in  FIG.  4   . 
     The gas sensor apparatus  150  includes the transmission unit  13 . The transmission unit  13  is configured to transmit the first calibration information Ic′ to the second gas sensor apparatus  250 . The first calibration information Ic′ is calibration information for calibrating the concentration of the gas  503  (see  FIG.  1   ) in the measurement target  501  (see  FIG.  7   ) which is calculated based on the output of the first gas sensor  11 . The first gas sensor apparatus  100  may be subjected to self-calibration, or may be calibrated based on another sensor (for example, the gas sensor  600  (see FIG.  7 )). 
     The gas sensor apparatus  250  includes the reception unit  20  and the calibration unit  24 . The reception unit  20  is configured to receive the first calibration information Ic′. The calibration unit  24  is configured to calibrate, based on the first calibration information Ic′ received by the reception unit  20 , the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . 
     The gas sensor apparatus  150  may include or may not include the first gas sensor  11 . In the present example, the gas sensor apparatus  150  includes the first gas sensor  11 . The gas sensor apparatus  250  may include or may not include the second gas sensor  21 . In the present example, the gas sensor apparatus  250  includes the second gas sensor  21 . When the gas sensor apparatus  150  is a mobile terminal, the first gas sensor  11  may be provided in the gas sensor apparatus  150 . When the gas sensor apparatus  250  is a mobile terminal, the second gas sensor  21  may be provided in the gas sensor apparatus  250 . 
     When the living body  90  (see  FIG.  7   ) having the first gas sensor apparatus  150  remains in the measurement target  501 , the transmission unit  13  may transmit the first calibration information Ic′ to an open space in the measurement target  501 . When the living body  90  has moved to the measurement target  502  (see  FIG.  1   ), the transmission unit  13  may transmit the first calibration information Ic′ to the interior space  508 . The transmission unit  13  may wirelessly transmit the first calibration information Ic′. 
     Similarly as in the examples illustrated in  FIG.  1    and  FIG.  2   , the measurement target  502  in which the concentration C 1 ′ is calculated based on the output of the first gas sensor  11  and the measurement target  502  in which the concentration C 2  is calculated based on the output of the second gas sensor  21  may be the same. A situation where the measurement target  502  in which the concentration C 1 ′ is calculated and the measurement target  502  in which the concentration C 2  is calculated are the same may refer to a situation where a type of the measurement target gas of the first gas sensor apparatus  150  and a type of the measurement target gas of the second gas sensor apparatus  250  are the same in the measurement target  502  as described above. The measurement target gas of the first gas sensor apparatus  150  and the second gas sensor apparatus  250  may be CO 2  (carbon dioxide), may be CH 4  methane, or may be alcohol. 
     A situation where the measurement target  502  in which the concentration C 1 ′ is calculated is the same as the measurement target  502  in which the concentration C 2  is calculated may refer to a situation where the first gas sensor  11  and the second gas sensor  21  share a same space (in the present example, the interior space  508  (see  FIG.  7   )) as described above. The same space may refer to at least one of a case where a temperature or a humidity in the space is the same, a case where an ID of short distance radio (Wi-Fi (registered trademark) or the like) is the same, or a case where, when the gas sensor apparatus  150  and the gas sensor apparatus  250  are a mobile terminal, an amplitude and a frequency of acoustic waves acquired by the mobile terminal are the same. 
     The second gas sensor  21  may be arranged in the interior space  508  (see  FIG.  7   ). In the present example, the gas sensor apparatus  250  includes the second gas sensor  21 , and the gas sensor apparatus  250  is arranged in the interior space  508 . 
     The transmission unit  13  may transmit the reliability information Ir 1  indicating the calibration reliability R 1  of the first gas sensor apparatus  150  to the second gas sensor apparatus  250 . The reception unit  20  may receive the reliability information Ir 1 . The calibration unit  24  may calibrate, based on the first calibration information Ic′ and the calibration reliability R 1  of the first gas sensor apparatus  150 , the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . The calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21  according to the reliability information Ir 1 . 
     When the reliability of the self-calibration of the second gas sensor apparatus  250  is equal to or lower than the second threshold Rth 2  and also the calibration reliability R 1  exceeds the first threshold Rth 1 , the calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . A case where the reliability of the self-calibration of the second gas sensor apparatus  250  is equal to or lower than the second threshold Rth 2  may include a case where the second gas sensor apparatus  250  does not have a function of the self-calibration. 
     The calibration unit  24  may compare the calibration reliability R 1  of the first gas sensor apparatus  150  which is received by the reception unit  20  with the calibration reliability R 2  of the second gas sensor apparatus  250 . The calibration reliability R 2  of the second gas sensor apparatus  250  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  250  and the calibration reliability R 2  in a case where the second gas sensor apparatus  250  is calibrated by another sensor. 
     When the calibration reliability R 1  is higher than the calibration reliability R 2 , the calibration unit  24  may calibrate, based on the first calibration information Ic′ received by the reception unit  20 , the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . When the calibration reliability R 1  is higher than the calibration reliability R 2 , since the concentration of the gas  504  is calibrated, the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  is likely to be accurate. When the calibration reliability R 1  is equal to or lower than the calibration reliability R 2 , a configuration may be adopted where the calibration unit  24  does not calibrate the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 , or the calibration unit  24  may calibrate the concentration of the gas  504  based on the second calibration information Ic“. The second calibration information Ic” is calibration information for calibrating the concentration of the gas  504  (see  FIG.  7   ) in the measurement target  502  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . 
     The gas sensor apparatus  250  may further include the storage unit  122 . The calibration reliability R 1  of the first gas sensor apparatus  150  which is received by the reception unit  20  may be stored in the storage unit  122 . The calibration reliability R 1  stored in the storage unit  122  may refer to a past calibration reliability of the first gas sensor apparatus  150 . The calibration unit  24  may compare the calibration reliability R 1  stored in the storage unit  122  with a current calibration reliability R 1  of the first gas sensor apparatus  150  which is received by the reception unit  20 . When the current calibration reliability R 1  is higher than the calibration reliability R 1  which is stored in the storage unit  122 , the calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . 
     When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received by the reception unit  20  is higher than the reference calibration reliability Cs, the calibration unit  24  may calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . The storage unit  122  may store the reference reliability information Cs. When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received by the reception unit  20  is higher than the reference calibration reliability Cs, the storage unit  122  may update the reference calibration reliability Cs based on the received calibration reliability R 1  and store the updated reference calibration reliability Cs. The calibration unit  24  may calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21  according to the updated reference reliability Cs. 
     When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received by the reception unit  20  is higher than the reference calibration reliability Cs, the storage unit  122  may update the reference calibration reliability Cs to the received calibration reliability R 1  and store the updated reference calibration reliability Cs. When the calibration reliability R 1  is lower than the reference calibration reliability Cs, a configuration may be adopted where the storage unit  122  does not update the reference calibration reliability Cs. 
     The reference reliability information Cs stored in the storage unit  122  may be the reference reliability information Cs updated based on the calibration reliability R 1  or may be the calibration reliability R 2 . The calibration reliability R 2  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  250  and the calibration reliability R 2  in a case where the second gas sensor apparatus  200  is calibrated by another sensor. 
     The gas sensor apparatus  150  may further include the position information acquisition unit  16 . The gas sensor apparatus  250  may further include the position information acquisition unit  26 . The position information acquisition unit  16  is configured to acquire information of a position of the first gas sensor apparatus  150 . The position information acquisition unit  26  is configured to acquire information of a position of the second gas sensor apparatus  250 . The position information acquisition unit  16  and the position information acquisition unit  26  are, for example, a global positioning system (GPS). 
     The position information of the first gas sensor apparatus  150  is set as the position information Ip 1 . The reliability information Ir 1  may include the position information Ip 1 . The position information of the second gas sensor apparatus  250  is set as the position information Ip 2 . The reliability information Ir 2  may include the position information Ip 2 . 
     The calibration unit  24  may calibrate, based on the distance d between the position of the first gas sensor apparatus  150  and the position of the second gas sensor apparatus  250  and the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . As described above, the predetermined distance between the position of the first gas sensor  11  and the position of the second gas sensor  21  is the distance dp 2 . When the distance d is less than the distance dp 2 , the calibration unit  24  may calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21 . As described above, the distance dp 2  may refer to a distance at which likelihood that the first gas sensor  11  and the second gas sensor  21  are arranged in a same space (for example, the interior space  508  of  FIG.  7   ) is high. 
     When the distance d exceeds the distance dp 2 , a configuration may be adopted where the calibration unit  24  does not calibrate the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21 . The calibration unit  24  may calibrate, based on the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21  according to the distance d. 
       FIG.  9    is a block diagram illustrating another example of the gas sensor apparatus  150  and the gas sensor apparatus  250  according to an embodiment of the present invention. In the present example, a plurality of the gas sensor apparatuses  150  (a gas sensor apparatus  150 - 1  to a gas sensor apparatus  150 - n ) are arranged in the measurement target  501 , and the single gas sensor apparatus  250  is arranged in the measurement target  502 . The gas sensor apparatus  150  may be the same as the first gas sensor apparatus  100  illustrated in  FIG.  5   . The gas sensor apparatus  250  may be the same as the second gas sensor apparatus  200  illustrated in  FIG.  5   . 
     The transmission unit  13 - 1  to the transmission unit  13 - n  (see  FIG.  8   ) respectively included in the gas sensor apparatus  150 - 1  to the gas sensor apparatus  150 - n  may respectively transmit the first calibration information Ic′ 1  to the first calibration information Ic′n. When the plurality of living bodies  90  (see  FIG.  7   ) have moved to the measurement target  502 , the transmission unit  13 - 1  to the transmission unit  13 - n  may respectively transmit the first calibration information Ic′ 1  to the first calibration information Ic′n to the interior space  508  (see  FIG.  7   ). 
     The reception unit  20  of the gas sensor apparatus  250  may receive the first calibration information Ic′ of each of the plurality of gas sensor apparatuses  150 . In the present example, the reception unit  20  receives the first calibration information Ic′ 1  to the first calibration information Ic′n respectively transmitted by the transmission unit  13 - 1  to the transmission unit  13 - n  (see  FIG.  8   ). 
     The calibration unit  24  of the gas sensor apparatus  250  may calibrate, based on the plurality of first calibration information Ic′, the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . In the present example, the calibration unit  24  calibrates the concentration of the gas  504  based on the first calibration information Ic′ 1  to the first calibration information Ic′n. As a result, the concentration of the gas  504  is more likely to be calibrated to an accurate concentration as compared with a case where the concentration of the gas  504  is calibrated based on one piece of the first calibration information Ic′. 
     The transmission unit  13  (see  FIG.  8   ) of each of the plurality of gas sensor apparatuses  150  may transmit the reliability information Ir 1  of each of the first gas sensor apparatuses  150 . In the present example, the transmission unit  13 - 1  to the transmission unit  13 - n  respectively transmit the reliability information Ir 1 - 1  to the reliability information Ir 1 - n.    
     The reception unit  20  may receive the reliability information Ir 1  of each of the plurality of first gas sensor apparatuses  150 . In the present example, the reception unit  20  receives the reliability information Ir 1 - 1  to the reliability information Ir 1 - n . The reliability information Ir 1 - 1  to the reliability information Ir 1 - n  may be stored in the storage unit  122 . 
     The calibration unit  24  may apply a weighting to the calibration reliability R 11  to the calibration reliability R 1   n  of each of the plurality of first gas sensor apparatuses  150 . The calibration unit  24  may calibrate, based on the calibration reliability R 1  to which the weighting has been applied, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . As a result, the concentration of the gas  504  is more likely to be calibrated to an accurate concentration as compared with a case where the concentration of the gas  504  is calibrated based on the calibration reliability R 1  on which no weighting has been applied. The calibration unit  24  may calibrate, based on a highest calibration reliability R 1  among the calibration reliability R 11  to the calibration reliability R 1   n , the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . 
       FIG.  10    is a flowchart illustrating an example of a gas sensor calibration method according to an embodiment of the present invention. The gas sensor calibration method according to an embodiment of the present invention will be described by using the gas sensor system  400  illustrated in  FIG.  4    and  FIG.  5    as an example. 
     Transmission step S 100  is a step for the transmission unit  13  to transmit the first calibration information Ic′. The first calibration information Ic′ is calibration information for calibrating the concentration of the gas  503  (see  FIG.  1   ) in the measurement target  501  (see  FIG.  1   ) which is calculated based on the output of the first gas sensor  11 . 
     Reception step S 102  is a step for the reception unit  20  to receive the first calibration information Ic′ transmitted in the transmission step S 100 . Calibration step S 104  is a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . 
     The transmission step S 100  may be a step for the transmission unit  13  to further transmit the reliability information Ir 1  indicating the calibration reliability R 1  of the first gas sensor apparatus  100 . The reception step S 102  may be a step for the reception unit  20  to further receive the reliability information Ir 1  transmitted in the transmission step S 100 . 
     The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ and the reliability information Ir 1 , the gas concentration of the gas  504  in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  according to the calibration reliability R 1 . 
     When the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  is equal to or lower than the predetermined second threshold Rth 2  and also the calibration reliability R 1  exceeds the first threshold Rth 1 , the calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . 
     The calibration step S 104  may be a step for the calibration unit  24  to compare the calibration reliability R 1  received in the reception step S 102  with the calibration reliability R 2 , and when the calibration reliability R 1  is higher than the calibration reliability R 2 , to calibrate, based on the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received in the reception step S 102  is higher than the reference calibration reliability Cs, the calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . 
       FIG.  11    illustrates an example of a detail of the calibration step S 104  in  FIG.  10   . AD conversion step S 90  is a step for the AD conversion unit  124  to convert an output of an analog signal of the second gas sensor  21  into a digital signal. Computation step S 92  is a step for the computation unit  120  to calculate the concentration of the gas  504  based on the digital signal converted in the AD conversion step S 90 . Storage step S 94  is a step for the storage unit  112  to store the concentration of the gas  504  which is calculated in the computation step S 92 . The storage step S 94  may be a step of storing the correlation Cr′ between the concentration of the gas  504  which is calculated in the computation step S 92  and the first calibration information Ic′. 
     Computation step S 96  is a step for the computation unit  120  to compute the second calibration information Ic″ based on the first calibration information Ic′ received in the reception step S 102  and the correlation Cr′ stored in the storage step S 94 . Calibration step S 98  based on a digital signal is a step for the calibration unit  24  (see  FIG.  4   ) to calibrate, by the second calibration information Ic″ of the digital signal, the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . Note that the computation step S 96  may be a step for the calibration unit  24  to perform calibration while calculating the concentration of the gas  504  based on the digital signal converted in the AD conversion step S 90  and the first calibration information Ic′ received in the reception step S 102 . 
     When the living body  90  (see  FIG.  1   ) having the first gas sensor apparatus  100  has moved from the measurement target  501  to the measurement target  502 , the measurement target  502  in which the concentration of the gas  504  is calculated based on the output of the first gas sensor  11  may be the same as the measurement target  502  in which the concentration of the gas  504  is calculated based on the output of the second gas sensor  21 . A situation where the measurement target  502  is the same may refer to a situation where a type of the measurement target gas of the first gas sensor apparatus  100  is the same as a type of the measurement target gas of the second gas sensor apparatus  200  in the measurement target  502 . In the present example, the second gas sensor apparatus  200  is arranged in the interior space  508 . 
     A situation where the measurement target  502  is the same may refer to a situation where the first gas sensor  11  and the second gas sensor  21  share a same space (in the present example, the interior space  508  (see  FIG.  1   )). The same space may refer to at least one of a case where a temperature or a humidity in the space is the same, a case where an ID of short distance radio (Wi-Fi (registered trademark) or the like) is the same, or a case where, when the first gas sensor apparatus  100  and the second gas sensor apparatus  200  are a mobile terminal, an amplitude and a frequency of acoustic waves acquired by the mobile terminal are the same. 
     The storage unit  122  may store the reference reliability information Cs. When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received in the reception step S 102  is higher than the reference calibration reliability Cs, the storage step S 94  may include update step S 941  for the storage unit  122  to update the reference calibration reliability Cs based on the received calibration reliability R 1 . In the storage step S 94 , the storage unit  122  may store the updated reference calibration reliability Cs. The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21  according to the updated reference reliability Cs. 
     When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received in the reception step S 102  is higher than the reference calibration reliability Cs, the update step S 941  may be a step for the storage unit  122  to update the reference calibration reliability Cs to the calibration reliability R 1 . When the calibration reliability R 1  is lower than the reference calibration reliability Cs, in the storage step S 94 , a configuration may be adopted where the storage unit  122  does not update the reference calibration reliability Cs. 
     The reference reliability information Cs stored in the storage step S 94  may be the reference reliability information Cs updated based on the calibration reliability R 1 , or may be the calibration reliability R 2 . The calibration reliability R 2  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  and the calibration reliability R 2  in a case where the second gas sensor apparatus  200  is calibrated by another sensor. 
       FIG.  12    is a flowchart illustrating another example of the gas sensor calibration method according to an embodiment of the present invention. The gas sensor calibration method of the present example is different from the gas sensor calibration method illustrated in  FIG.  10    in that storage step S 1031  and position information acquisition step S 1032  are further included. The gas sensor calibration method of the present example will be described by using the gas sensor system  400  illustrated in  FIG.  4    and  FIG.  5    as an example. 
     The storage step S 1031  is a step for the storage unit  122  to store the reliability information Ir 1  received in the reception step S 102 . The calibration step S 104  is a step for the calibration unit  24  to compare the reliability information Ir 1  received in the reception step S 102  with the reliability information Ir 1  stored in the storage step S 1031 , and when the reliability information Ir 1  received in the reception step S 102  is higher than the reliability information Ir 1  stored in the storage step S 1031 , to calibrate, based on the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . The calibration step S 104  may be performed after the storage step S 1031 . 
     When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received in the reception step S 102  is higher than the reference calibration reliability Cs, the storage step S 1031  may include update step S 1033  for the storage unit  122  to update the reference calibration reliability Cs based on the received calibration reliability R 1 . In storage step S 1031 , the storage unit  122  may store the updated reference calibration reliability Cs. The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21  according to the updated reference reliability Cs. 
     When the calibration reliability R 1  of the first gas sensor apparatus  100  which is received in the reception step S 102  is higher than the reference calibration reliability Cs, the update step S 1033  may be a step for the storage unit  122  to update the reference calibration reliability Cs to the calibration reliability R 1 . When the calibration reliability R 1  is lower than the reference calibration reliability Cs, in the storage step S 1031 , a configuration may be adopted where the storage unit  122  does not update the reference calibration reliability Cs. 
     The reference reliability information Cs stored in the storage step S 1031  may be the reference reliability information Cs updated based on the calibration reliability R 1 , or may be the calibration reliability R 2 . The calibration reliability R 2  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  200  and the calibration reliability R 2  in a case where the second gas sensor apparatus  200  is calibrated by another sensor. 
     The position information acquisition step S 1032  is a step for the position information acquisition unit  26  to acquire the position information Ip 2  of the second gas sensor apparatus  200 . In the position information acquisition step S 1032 , the position information acquisition unit  16  may acquire the position information Ip 1  of the first gas sensor apparatus  100 . The position information acquisition unit  16  and the position information acquisition unit  26  are, for example, a global positioning system (GPS). 
     The reliability information Ir 1  may include the position information Ip 1 . As described above, the distance d is the distance between the position of the first gas sensor apparatus  100  and the position of the second gas sensor apparatus  200  which is acquired by the position information acquisition unit  26 . The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the distance d and the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  according to the distance d. The calibration step S 104  may be performed after the position information acquisition step S 1032 . 
     As described above, the distance dp 2  is the predetermined distance between the position of the first gas sensor  11  and the position of the second gas sensor  21 . When the distance d is less than the distance dp 2 , the calibration step S 104  may be a step for the calibration unit  24  to calibrate the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . In the calibration step S 104 , when the distance d is equal to or more than the distance dp 2 , a configuration may be adopted where the calibration unit  24  does not calibrate the concentration of the gas  504 , or the calibration unit  24  may calibrate the concentration of the gas  504  based on the second calibration information Ic“. The second calibration information Ic” is calibration information for calibrating the concentration of the gas  504  (see  FIG.  7   ) in the measurement target  502  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . 
     An order of the storage step S 1031  and the position information acquisition step S 1032  may be reversed. That is, after the reception step S 102 , the position information acquisition step S 1032  may be performed, and after the position information acquisition step S 1032 , the storage step S 1031  may be performed. When the order of the storage step S 1031  and the position information acquisition step S 1032  is reversed, the storage unit  122  may store the position information Ip 2 , or may store the position information Ip 2  and the position information Ip 1 . 
     The reception step S 102  may be a step for the reception unit  20  to receive the first calibration information Ic′ in each of the plurality of first gas sensor apparatuses  100 . The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on each of the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . In the present example, in the calibration step S 104 , the calibration unit  24  calibrates the concentration of the gas  504  based on the first calibration information Ic′ 1  to the first calibration information Ic′n. As a result, the concentration of the gas  504  is more likely to be calibrated to an accurate concentration as compared with a case where the concentration of the gas  504  is calibrated based on one piece of the first calibration information Ic′. 
     The transmission step S 100  may be a step for the transmission unit  13  to further transmit the reliability information Ir 1  of each of the plurality of first gas sensor apparatuses  100 . The reception step S 102  may be a step for the reception unit  20  to further receive the reliability information Ir 1  transmitted in the transmission step S 100 . The calibration step S 104  may be a step for the calibration unit  24  to apply a weighting to the calibration reliability R 11  to the calibration reliability R 1   n , and to calibrate, based on the calibration reliability R 1  to which the weighting has been applied, the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . 
     The storage step S 1031  may be a step of storing the reliability information Ir 1  of each of the plurality of first gas sensor apparatuses  100  which is received in the reception step S 102 . The computation step S 96  illustrated in  FIG.  11    may be a step for the computation unit  120  to compute a weighting of the calibration reliability R 11  to the calibration reliability R 1   n  based on each of the reliability information Ir 1  stored in the storage step S 1031 , and also to compute the second calibration information Ic″ by applying the weighting to the calibration reliability R 11  to the calibration reliability R 1   n.    
     The calibration step S 98  based on the digital signal which is illustrated in  FIG.  11    may be a step for the calibration unit  24  (see  FIG.  4    and  FIG.  5   ) to calibrate the concentration of the gas  504  (see  FIG.  1   ) in the measurement target  502  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21  by the digital signal of the second calibration information Ic″ to which the weighting has been applied. As a result, the concentration of the gas  504  is more likely to be calibrated to an accurate concentration as compared with a case where the concentration of the gas  504  is calibrated based on the second calibration information Ic″ to which no weighting of the calibration reliability R 1  has been applied. 
     The calibration step S 104  may be a step for the calibration unit  24  to calibrate, based on the highest calibration reliability R 1  among the calibration reliability R 11  to the calibration reliability R 1   n , the concentration of the gas  504  (see  FIG.  1   ) which is calculated based on the output of the second gas sensor  21 . In the calibration step S 104 , the calibration unit  24  may calibrate the concentration of the gas  504  by setting a weighting of the highest calibration reliability R 1  as  1  and setting a weighting of the other calibration reliabilities R 1  as zero. 
       FIG.  13    is a flowchart illustrating an example of the gas sensor calibration method according to an embodiment of the present invention. The gas sensor calibration method according to an embodiment of the present invention will be described by using the gas sensor apparatus  150  illustrated in  FIG.  8    and  FIG.  9    as an example. 
     Transmission step S 200  is a step for the transmission unit  13  to transmit the first calibration information Ic′ to the second gas sensor apparatus  250 . The first calibration information Ic′ is calibration information for calibrating the concentration of the gas  503  (see  FIG.  7   ) in the measurement target  501  (see  FIG.  7   ) which is calculated based on the output of the first gas sensor  11 . The transmission step S 200  may be a step for the transmission unit  13  to further transmit the reliability information Ir 1  indicating the calibration reliability R 1  of the first gas sensor apparatus  150  to the second gas sensor apparatus  250 . 
       FIG.  14    is a flowchart illustrating an example of the gas sensor calibration method according to an embodiment of the present invention. The gas sensor calibration method according to an embodiment of the present invention will be described by using the gas sensor apparatus  250  illustrated in  FIG.  8    and  FIG.  9    as an example. 
     Reception step S 302  is a step for the reception unit  20  to receive the first calibration information Ic′ of the first gas sensor apparatus  150 . Calibration step S 304  is a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 102 , the concentration of the gas  504  (see  FIG.  7   ) in the measurement target  502  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . 
     According to the gas sensor calibration method illustrated in  FIG.  13    and  FIG.  14   , when the living body  90  (see  FIG.  7   ) having the first gas sensor apparatus  150  has moved from the measurement target  501  to the measurement target  502 , the measurement target  502  in which the concentration of the gas  504  is calculated based on the output of the first gas sensor  11  may be the same as the measurement target  502  in which the concentration of the gas  504  is calculated based on the output of the second gas sensor  21 . A situation where the measurement target  502  is the same may refer to a situation where a type of the measurement target gas of the first gas sensor apparatus  150  is the same as a type of the measurement target gas of the second gas sensor apparatus  250  in the measurement target  502  as described above. In the present example, the second gas sensor apparatus  250  is arranged in the interior space  508 . 
     A situation where the measurement target  502  is the same may refer to a situation where the first gas sensor  11  and the second gas sensor  21  share a same space (in the present example, the interior space  508  (see  FIG.  7   )) as described above. The same space may refer to at least one of a case where a temperature or a humidity in the space is the same, a case where an ID of short distance radio (Wi-Fi (registered trademark) or the like) is the same, or a case where, when the first gas sensor apparatus  150  and the second gas sensor apparatus  250  are a mobile terminal, an amplitude and a frequency of acoustic waves acquired by the mobile terminal are the same. 
     The reception step S 302  may be a step for the reception unit  20  to further receive the reliability information Ir 1  indicating the calibration reliability R 1 . The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ and the reliability information Ir 1 , the gas concentration of the gas  504  in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 302 , the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  according to the calibration reliability R 1 . 
     When the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  250  is equal to or lower than the predetermined second threshold Rth 2  and also the calibration reliability R 1  exceeds the first threshold Rth 1 , the calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 302 , the concentration of the gas  504  in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . 
     The calibration step S 304  may be a step for the calibration unit  24  to compare the calibration reliability R 1  of the first gas sensor apparatus  150  with the calibration reliability R 2 , and when the calibration reliability R 1  is higher than the calibration reliability R 2 , to calibrate, based on the first calibration information Ic′ received in the reception step S 302 , the concentration of the gas  504  in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received in the reception step S 302  is higher than the reference calibration reliability Cs, the calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21 . 
       FIG.  15    illustrates an example of a detail of the calibration step S 304  in  FIG.  14   . AD conversion step S 190  is a step for the AD conversion unit  124  to convert an output of an analog signal of the second gas sensor  21  into a digital signal. Computation step S 192  is a step for the computation unit  120  to calculate the concentration of the gas  504  based on the digital signal converted in the AD conversion step S 190 . Storage step S 194  is a step for the storage unit  112  to store the concentration of the gas  504  which is calculated in the computation step S 192 . The storage step S 194  may be a step of storing the correlation Cr′ between the concentration of the gas  504  which is calculated in the computation step S 192  and the first calibration information Ic′. 
     Computation step S 196  is a step for the computation unit  120  to compute the second calibration information Ic″ based on the first calibration information Ic′ received in the reception step S 302  and the correlation Cr′ stored in the storage step S 194 . Calibration step S 198  based on a digital signal is a step for the calibration unit  24  (see  FIG.  4   ) to calibrate, based on the second calibration information Ic″ of the digital signal, the concentration of the gas  504  (see  FIG.  7   ) in the measurement target  502  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . Note that the computation step S 196  may be a step for the calibration unit  24  to perform calibration while calculating the concentration of the gas  504  based on the digital signal converted in the AD conversion step S 190  and the second calibration information Ic″ received in the reception step S 302 . 
     The storage unit  122  may store the reference reliability information Cs. When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received in the reception step S 302  is higher than the reference calibration reliability Cs, the storage step S 194  may include update step S 1941  for the storage unit  122  to update the reference calibration reliability Cs based on the received calibration reliability R 1 . In the storage step S 194 , the storage unit  122  may store the updated reference calibration reliability Cs. The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21  according to the updated reference reliability Cs. 
     When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received in the reception step S 302  is higher than the reference calibration reliability Cs, the update step S 1941  may be a step for the storage unit  122  to update the reference calibration reliability Cs to the calibration reliability R 1 . In the storage step S 194 , when the calibration reliability R 1  is lower than the reference calibration reliability Cs, a configuration may be adopted where the storage unit  122  does not update the reference calibration reliability Cs. 
     The reference reliability information Cs stored in the storage step S 194  may be the reference reliability information Cs updated based on the calibration reliability R 1  or may be the calibration reliability R 2 . The calibration reliability R 2  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  250  and the calibration reliability R 2  in a case where the second gas sensor apparatus  250  is calibrated by another sensor. 
       FIG.  16    is a flowchart illustrating another example of the gas sensor calibration method according to an embodiment of the present invention. The gas sensor calibration method of the present example is different from the gas sensor calibration method illustrated in  FIG.  14    in that storage step S 3031  and position information acquisition step S 3032  are further included. The gas sensor calibration method of the present example will be described by using the gas sensor apparatus  250  illustrated in  FIG.  8    and  FIG.  9    as an example. 
     The storage step S 3031  is a step for the storage unit  122  to store the reliability information Ir 1  received in the reception step S 302 . The calibration step S 304  is a step for the calibration unit  24  to compare the reliability information Ir 1  received in the reception step S 302  with the reliability information Ir 1  stored in the storage step S 3031 , and when the reliability information Ir 1  received in the reception step S 302  is higher than the reliability information Ir 1  stored in the storage step S 3031 , to calibrate, based on the first calibration information Ic′ received in the reception step S 302 , the concentration of the gas  504  (see  FIG.  7   ) in the measurement target  502  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . The calibration step S 304  may be performed after the storage step S 3031 . 
     When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received in the reception step S 102  is higher than the reference calibration reliability Cs, the storage step S 3031  may include update step S 3033  for the storage unit  122  to update the reference calibration reliability Cs based on the received calibration reliability R 1 . In the storage step S 3031 , the storage unit  122  may store the updated reference calibration reliability Cs. The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′, the gas concentration in the measurement target  502  which is calculated based on the output of the second gas sensor  21  according to the updated reference reliability Cs. 
     When the calibration reliability R 1  of the first gas sensor apparatus  150  which is received in the reception step S 302  is higher than the reference calibration reliability Cs, the update step S 3033  may be a step for the storage unit  122  to update the reference calibration reliability Cs to the calibration reliability R 1 . In the storage step S 3031 , when the calibration reliability R 1  is lower than the reference calibration reliability Cs, a configuration may be adopted where the storage unit  122  does not update the reference calibration reliability Cs. 
     The reference reliability information Cs stored in the storage step S 3031  may be the reference reliability information Cs updated based on the calibration reliability R 1 , or may be the calibration reliability R 2 . The calibration reliability R 2  may include the calibration reliability R 2  of the self-calibration of the second gas sensor apparatus  250  and the calibration reliability R 2  in a case where the second gas sensor apparatus  250  is calibrated by another sensor. 
     The position information acquisition step S 3032  is a step for the position information acquisition unit  26  to acquire the position information Ip 2  of the second gas sensor apparatus  200 . In the position information acquisition step S 3032 , the position information acquisition unit  16  may acquire the position information Ip 1  of the first gas sensor apparatus  100 . The position information acquisition unit  16  and the position information acquisition unit  26  are, for example, a global positioning system (GPS). 
     The reliability information Ir 1  may include the position information Ip 1 . As described above, the distance d is the distance between the position of the first gas sensor apparatus  100  and the position of the second gas sensor apparatus  200  which is acquired by the position information acquisition unit  26 . The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the distance d and the first calibration information Ic′, the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the first calibration information Ic′ received in the reception step S 302 , the concentration of the gas  504  which is calculated based on the output of the second gas sensor  21  according to the distance d. The calibration step S 304  may be performed after the position information acquisition step S 3032 . 
     As described above, the distance dp 2  is the predetermined distance between the position of the first gas sensor  11  and the position of the second gas sensor  21 . When the distance d is less than the distance dp 2 , the calibration step S 304  may be a step for the calibration unit  24  to calibrate the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . In the calibration step S 304 , when the distance d is equal to or more than the distance dp 2 , a configuration may be adopted where the calibration unit  24  does not calibrate the concentration of the gas  504 . 
     An order of the storage step S 3031  and the position information acquisition step S 3032  may be reversed. That is, after the reception step S 302 , the position information acquisition step S 3032  may be performed, and after the position information acquisition step S 3032 , the storage step S 3031  may be performed. When the order of the storage step S 3031  and the position information acquisition step S 3032  is reversed, the storage unit  122  may store the position information Ip 2 , or may store the position information Ip 2  and the position information Ip 1 . 
     The reception step S 302  may be a step for the reception unit  20  to receive the first calibration information Ic′ in each of the plurality of first gas sensor apparatuses  100 . The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on each of the first calibration information Ic′ received in the reception step S 302 , the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . In the present example, in the calibration step S 304 , the calibration unit  24  calibrates the concentration of the gas  504  based on the first calibration information Ic′ 1  to the first calibration information Ic′n. As a result, the concentration of the gas  504  is more likely to be calibrated to an accurate concentration as compared with a case where the concentration of the gas  504  is calibrated based on one piece of the first calibration information Ic′. 
     The reception step S 302  may be a step for the reception unit  20  to further receive the reliability information Ir 1  of each of the plurality of first gas sensor apparatuses  100 . The calibration step S 304  may be a step for the calibration unit  24  to apply a weighting to the calibration reliability R 11  to the calibration reliability R 1   n , and to calibrate, based on the calibration reliability R 1  to which the weighting has been applied, the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . 
     The storage step S 3031  may be a step of storing the reliability information Ir 1  of each of the plurality of first gas sensor apparatuses  100  which is received in the reception step S 302 . The computation step S 196  illustrated in  FIG.  15    may be a step for the computation unit  120  to compute a weighting of the calibration reliability R 11  to the calibration reliability R 1   n  based on each of the reliability information Ir 1  stored in the storage step S 3031 , and also to compute the second calibration information Ic″ by applying the weighting to the calibration reliability R 11  to the calibration reliability R 1   n.    
     The calibration step S 198  based on the digital signal which is illustrated in  FIG.  15    may be a step for the calibration unit  24  (see  FIG.  8    and  FIG.  9   ) to calibrate the concentration of the gas  504  (see  FIG.  7   ) in the measurement target  502  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21  by the digital signal of the second calibration information Ic″ to which the weighting has been applied. As a result, the concentration of the gas  504  is more likely to be calibrated to an accurate concentration as compared with a case where the concentration of the gas  504  is calibrated based on the second calibration information Ic″ to which no weighting of the calibration reliability R 1  has been applied. 
     The calibration step S 304  may be a step for the calibration unit  24  to calibrate, based on the highest calibration reliability R 1  among the calibration reliability R 11  to the calibration reliability R 1   n , the concentration of the gas  504  (see  FIG.  7   ) which is calculated based on the output of the second gas sensor  21 . In the calibration step S 304 , the calibration unit  24  may calibrate the concentration of the gas  504  by setting a weighting of the highest calibration reliability R 1  as  1  and setting a weighting of the other calibration reliabilities R 1  as zero. 
     Various embodiments of the present invention may be described with reference to flowcharts and block diagrams. According to the various embodiments of the present invention, a block may represent (1) a step of a process where operations are executed or (2) a section of an apparatus having a role for executing operations. 
     A specific step may be executed by a dedicated circuit, a programmable circuit, or a processor. A specific section may be implemented by a dedicated circuit, a programmable circuit, or a processor. The programmable circuit and the processor may be supplied together with a computer-readable instruction. The computer-readable instruction may be stored on a computer-readable medium. 
     The dedicated circuit may include at least one of a digital hardware circuit or an analog hardware circuit. The dedicated circuit may include at least one of an integrated circuit (IC) or a discrete circuit. The programmable circuit may include a hardware circuit including logical AND, logical OR, logical XOR, logical NAND, logical NOR, or other logical operations. The programmable circuit may include a reconfigurable hardware circuit including a flip-flop, a register, a memory element such as a field programmable gate array (FPGA) and a programmable logic array (PLA), and the like. 
     Computer-readable media may include any tangible device that can store instructions for execution by a suitable device. Since the computer-readable medium includes the tangible device, the computer-readable medium having the instruction stored on the device constitutes a product including an instruction that may be executed in order to provide means to execute an operation specified by a flowchart or a block diagram. 
     The computer-readable medium may be, for example, an electronic storage medium, a magnetic storage medium, an optical storage medium, an electromagnetic storage medium, a semiconductor storage medium, or the like. More specifically, for example, the computer-readable medium may be a floppy disk, a diskette, a hard disk, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM or flash memory), an electrically erasable programmable read only memory (EEPROM), a static random access memory (SRAM), a compact disk read only memory (CD-ROM), a digital versatile disk (DVD), a Blu-ray (registered trademark) disk, a memory stick, an integrated circuit card, or the like. 
     The computer-readable instruction may include any of an assembler instruction, an instruction-set-architecture (ISA) instruction, a machine instruction, a machine dependent instruction, a microcode, a firmware instruction, state-setting data, a source code, and an object code. The source code and the object code may be written in any combination of one or more programming languages including an object-oriented programming language and a procedural programming language in related art. The object-oriented programming language may be, for example, Smalltalk (registered trademark), JAVA (registered trademark), C++, or the like. The procedural programming language may be, for example, a “C” programming language. 
     The computer-readable instruction may be provided to a general purpose computer, a special purpose computer, or a processor or a programmable circuit of another programmable data processing apparatus locally or via a local area network (LAN) or a wide area network (WAN) such as the Internet. A processor or programmable circuitry of a general purpose computer, a special purpose computer, or another programmable data processing apparatus may perform a computer-readable instruction in order to create means configured to perform operations designated by the flowchart illustrated in  FIG.  10    to  FIG.  16    or the block diagram illustrated in  FIG.  2    to  FIG.  5   ,  FIG.  8   , or  FIG.  9   . The processor may be, for example, a computer processor, a processing unit, a microprocessor, a digital signal processor, a controller, a microcontroller, or the like. 
       FIG.  17    illustrates an example of a computer  2200  in which the gas sensor system  400 , the gas sensor apparatus  150 , or the gas sensor apparatus  250  according to an embodiment of the present invention may be entirely or partially embodied. A program installed in the computer  2200  can cause the computer  2200  to perform operations associated with the gas sensor apparatus  150  or the gas sensor apparatus  250  according to an embodiment of the present invention or function as one or more sections of the gas sensor apparatus  150  or the gas sensor apparatus  250  or to perform the operations or the one or more sections, or can cause the computer  2200  to perform each of steps (see  FIG.  10    to  FIG.  16   ) according to the gas sensor calibration method of the present invention. The program may be executed by a CPU  2212  in order to cause the computer  2200  to perform particular operations associated with the flowcharts ( FIG.  10    to  FIG.  16   ) and some or all of blocks in the block diagrams ( FIG.  2    to  FIG.  5   ,  FIG.  8   , or  FIG.  9   ) which are described in the present specification. 
     The computer  2200  according to an embodiment of the present invention includes the CPU  2212 , a RAM  2214 , a graphics controller  2216 , and a display device  2218 . The CPU  2212 , the RAM  2214 , the graphics controller  2216 , and the display device  2218  are mutually connected by a host controller  2210 . The computer  2200  further includes input and output units such as a communication interface  2222 , a hard disk drive  2224 , a DVD-ROM drive  2226 , and an IC card drive. The communication interface  2222 , the hard disk drive  2224 , the DVD-ROM drive  2226 , and the IC card drive, and the like are connected to the host controller  2210  via an input and output controller  2220 . The computer further includes legacy input and output units such as a ROM  2230  and a keyboard  2242 . The ROM  2230 , the keyboard  2242 , and the like are connected to the input and output controller  2220  through an input and output chip  2240 . 
     The CPU  2212  is configured to operate according to programs stored in the ROM  2230  and the RAM  2214 , thereby controlling each unit. The graphics controller  2216  is configured to obtain image data generated by the CPU  2212  on a frame buffer or the like provided in the RAM  2214  or in the RAM  2214  itself to cause the image data to be displayed on the display device  2218 . 
     The communication interface  2222  is configured to communicate with other electronic devices via a network. The hard disk drive  2224  is configured to store programs and data used by the CPU  2212  within the computer  2200 . The DVD-ROM drive  2226  is configured to read the programs or the data from the DVD-ROM  2201 , and provide the read programs or data to the hard disk drive  2224  via the RAM  2214 . The IC card drive is configured to read programs and data from an IC card, or write programs and data to the IC card. 
     The ROM  2230  is configured to store a boot program or the like executed by the computer  2200  at the time of activation, or a program depending on the hardware of the computer  2200 . The input and output chip  2240  may connect various input and output units via a parallel port, a serial port, a keyboard port, a mouse port, or the like to the input and output controller  2220 . 
     A program is provided by computer-readable media such as the DVD-ROM  2201  or the IC card. The program is read from the computer-readable media, installed into the hard disk drive  2224 , RAM  2214 , or ROM  2230 , which are also examples of computer-readable media, and executed by the CPU  2212 . The information processing described in these programs is read into the computer  2200 , resulting in cooperation between a program and the above described various types of hardware resources. An apparatus or method may be constituted by realizing the operation or processing of information in accordance with the usage of the computer  2200 . 
     For example, when a communication is performed between the computer  2200  and an external device, the CPU  2212  may execute a communication program loaded onto the RAM  2214  to instruct the communication interface  2222  to perform communication processing based on the processing described in the communication program. The communication interface  2222 , under control of the CPU  2212 , reads transmission data stored on a transmission buffering region provided in a recording medium such as the RAM  2214 , the hard disk drive  2224 , the DVD-ROM  2201 , or the IC card, and transmits the read transmission data to a network or writes reception data received from a network to a reception buffering region or the like provided on the recording medium. 
     The CPU  2212  may cause all or a necessary portion of a file or a database to be read into the RAM  2214 , the file or the database having been stored in an external recording medium such as the hard disk drive  2224 , the DVD-ROM drive  2226  (DVD-ROM  2201 ), the IC card, or the like. The CPU  2212  may perform various types of processing on the data on the RAM  2214 . The CPU  2212  may then write back the processed data to the external recording medium. 
     Various types of information such as various types of programs, data, tables, and databases may be stored in the recording medium to undergo information processing. The CPU  2212  may perform various types of processing on the data read from the RAM  2214 , which includes various types of operations, processing of information, condition judging, conditional branch, unconditional branch, search or replace of information, or the like, as described throughout the present disclosure and designated by an instruction sequence of programs. The CPU  2212  may write the result back to the RAM  2214 . 
     The CPU  2212  may search for information in a file, a database, or the like in the recording medium. For example, when a plurality of entries, each having an attribute value of a first attribute associated with an attribute value of a second attribute, are stored in the recording medium, the CPU  2212  may search for an entry matching the condition whose attribute value of the first attribute is designated, from among the plurality of entries, read the attribute value of the second attribute stored in the entry, and read a second attribute value to obtain the attribute value of the second attribute associated with the first attribute satisfying the predetermined condition. 
     The above explained program or software modules may be stored in the computer-readable media on the computer  2200  or of the computer  2200 . A recording medium such as a hard disk or a RAM provided in a server system connected to a dedicated communication network or the Internet can be used as the computer-readable media. The program may be provided to the computer  2200  by the recording medium. 
     While the embodiments of the present invention have been described, the technical scope of the present invention is not limited to the above described embodiments. It is apparent to persons skilled in the art that various alterations and improvements can be added to the above described embodiments. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the present invention. 
     Note that the operations, procedures, steps, and stages of each process performed by an apparatus, system, program, and method shown in the claims, embodiments, or diagrams can be performed in any order as long as the order is not indicated by “prior to,” “before,” or the like and as long as the output from a previous process is not used in a later process. Even if the process flow is described using phrases such as “first” or “next” in the claims, embodiments, or diagrams, it does not necessarily mean that the process must be performed in this order. 
     Item 1 
     A gas sensor system comprising: 
     a first gas sensor apparatus including a transmission unit configured to transmit first calibration information for calibrating a gas concentration in a measurement target which is calculated based on an output of a first gas sensor; and 
     a second gas sensor apparatus including a reception unit configured to receive the first calibration information transmitted by the transmission unit, and a calibration unit configured to calibrate, based on the first calibration information received by the reception unit, a gas concentration in a measurement target which is calculated based on an output of a second gas sensor. 
     Item 2 
     The gas sensor system according to item 1, wherein the measurement target in which the gas concentration is calculated based on the output of the first gas sensor is the same as the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 3 
     The gas sensor system according to item 1 or 2, wherein 
     the first gas sensor apparatus includes the first gas sensor, and 
     the first gas sensor apparatus is a mobile terminal. 
     Item 4 
     The gas sensor system according to item 3, wherein the second gas sensor apparatus is arranged in an interior space in the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 5 
     The gas sensor system according to any one of items 1 to 4, wherein 
     the second gas sensor apparatus includes the second gas sensor, and 
     the second gas sensor apparatus is a mobile terminal. 
     Item 6 
     The gas sensor system according to any one of items 1 to 5, wherein 
     the transmission unit is configured to further transmit reliability information indicating a calibration reliability of the first gas sensor apparatus, 
     the reception unit is configured to further receive the reliability information, and 
     the calibration unit is configured to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to the calibration reliability of the first gas sensor apparatus. 
     Item 7 
     The gas sensor system according to item 6, wherein when a reliability of self-calibration of the second gas sensor apparatus is equal to or lower than a predetermined second threshold and also the calibration reliability of the first gas sensor apparatus exceeds a first threshold, the calibration unit is configured to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 8 
     The gas sensor system according to item 6 or 7, wherein the calibration unit is configured to compare the calibration reliability of the first gas sensor apparatus which is received by the reception unit with a calibration reliability of the second gas sensor apparatus, and when the calibration reliability of the first gas sensor apparatus is higher than the calibration reliability of the second gas sensor apparatus, to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 9 
     The gas sensor system according to any one of items 6 to 8, wherein 
     the second gas sensor apparatus further includes a storage unit configured to store the reliability information received by the reception unit, and 
     the calibration unit is configured to compare the calibration reliability of the first gas sensor apparatus which is received by the reception unit with the calibration reliability of the first gas sensor apparatus which is stored in the storage unit, and when the calibration reliability of the first gas sensor apparatus which is received by the reception unit is higher than the calibration reliability stored in the storage unit, to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 10 
     The gas sensor system according to any one of items 6 to 9, wherein 
     the second gas sensor apparatus further includes a position information acquisition unit configured to acquire information of a position of the second gas sensor apparatus, 
     the reliability information includes information of a position of the first gas sensor apparatus, and 
     the calibration unit is configured to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to a distance between the position of the first gas sensor apparatus and the position of the second gas sensor apparatus which is acquired by the position information acquisition unit. 
     Item 11 
     The gas sensor system according to item 10, wherein when the distance is less than a predetermined distance, the calibration unit is configured to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 12 
     The gas sensor system according to any one of items 6 to 11, comprising: 
     a plurality of the first gas sensor apparatuses, wherein 
     the reception unit is configured to receive first calibration information of each of the plurality of first gas sensor apparatuses, and 
     the calibration unit is configured to calibrate, based on the first calibration information of each of the plurality of first gas sensor apparatuses, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 13 
     The gas sensor system according to item 12, wherein 
     the transmission unit of each of the plurality of first gas sensor apparatuses is configured to transmit the reliability information of each of the first gas sensor apparatuses, 
     the reception unit is configured to receive the reliability information of each of the plurality of first gas sensor apparatuses, and 
     the calibration unit is configured to apply a weighting to the calibration reliability of each of the plurality of first gas sensor apparatuses, and to calibrate, based on the calibration reliability to which the weighting has been applied, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 14 
     The gas sensor system according to item 13, wherein the calibration unit is configured to calibrate, based on a highest calibration reliability among the calibration reliabilities of each of the plurality of first gas sensor apparatuses, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 15 
     A gas sensor apparatus comprising: 
     a transmission unit configured to transmit first calibration information to a second gas sensor apparatus, wherein 
     the first calibration information is calibration information for calibrating a gas concentration in a measurement target which is calculated based on an output of a first gas sensor. 
     Item 16 
     The gas sensor apparatus according to item 15, wherein 
     the second gas sensor apparatus includes a second gas sensor, and 
     the measurement target in which the gas concentration is calculated based on the output of the first gas sensor is the same as the measurement target in which a gas concentration is calculated based on an output of the second gas sensor. 
     Item 17 
     The gas sensor apparatus according to item 16, wherein the second gas sensor is provided in a mobile terminal. 
     Item 18 
     The gas sensor apparatus according to any one of items 15 to 17, wherein 
     the first gas sensor is provided in a first gas sensor apparatus, and 
     the transmission unit is configured to further transmit reliability information indicating a calibration reliability of the first gas sensor apparatus to the second gas sensor apparatus. 
     Item 19 
     A gas sensor apparatus comprising: 
     a reception unit configured to receive first calibration information of a first gas sensor apparatus; and 
     a calibration unit configured to calibrate, based on the first calibration information received by the reception unit, a gas concentration in a measurement target which is calculated based on an output of a second gas sensor. 
     Item 20 
     The gas sensor apparatus according to item 19, wherein 
     the first gas sensor apparatus includes a first gas sensor, and 
     a measurement target in which a gas concentration is calculated based on an output of the first gas sensor is the same as the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 21 
     The gas sensor apparatus according to item 20, wherein the first gas sensor is provided in a mobile terminal. 
     Item 22 
     The gas sensor apparatus according to item 21, wherein the second gas sensor is arranged in an interior space in the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 23 
     The gas sensor apparatus according to any one of items 19 to 22, wherein 
     the reception unit is configured to further receive reliability information indicating a calibration reliability of the first gas sensor apparatus, and 
     the calibration unit is configured to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to the calibration reliability of the first gas sensor apparatus. 
     Item 24 
     The gas sensor apparatus according to item 23, wherein 
     the second gas sensor is provided in a second gas sensor apparatus, and 
     when a reliability of self-calibration of the second gas sensor apparatus is equal to or lower than a predetermined second threshold and also the calibration reliability of the first gas sensor apparatus exceeds a first threshold, the calibration unit is configured to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 25 
     The gas sensor apparatus according to item 24, wherein the calibration unit is configured to compare the calibration reliability of the first gas sensor apparatus which is received by the reception unit with a calibration reliability of the second gas sensor apparatus, and when the calibration reliability of the first gas sensor apparatus is higher than the calibration reliability of the second gas sensor apparatus, to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 26 
     The gas sensor apparatus according to item 24 or 25, further comprising: 
     a storage unit configured to store the reliability information received by the reception unit, wherein 
     the calibration unit is configured to compare the calibration reliability of the first gas sensor apparatus which is received by the reception unit with the calibration reliability of the first gas sensor apparatus which is stored in the storage unit, and when the calibration reliability of the first gas sensor apparatus which is received by the reception unit is higher than the calibration reliability stored in the storage unit, to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 27 
     The gas sensor apparatus according to any one of items 24 to 26, further comprising: 
     a position information acquisition unit configured to acquire information of a position of the second gas sensor apparatus, wherein 
     the reliability information includes information of a position of the first gas sensor apparatus, and 
     the calibration unit is configured to calibrate, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to a distance between the position of the first gas sensor apparatus and the position of the second gas sensor apparatus which is acquired by the position information acquisition unit. 
     Item 28 
     The gas sensor apparatus according to item 27, wherein when the distance is less than a predetermined distance, the calibration unit is configured to calibrate the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 29 
     The gas sensor apparatus according to any one of items 23 to 28, wherein 
     the reception unit is configured to receive the first calibration information of each of the plurality of first gas sensor apparatuses, and 
     the calibration unit is configured to calibrate, based on the first calibration information of each of the plurality of first gas sensor apparatuses, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 30 
     The gas sensor apparatus according to item 29, wherein 
     the reception unit is configured to receive reliability information of each of the plurality of first gas sensor apparatuses, and 
     the calibration unit is configured to apply a weighting to the calibration reliability of each of the plurality of first gas sensor apparatuses, and to calibrate, based on the calibration reliability to which the weighting has been applied, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 31 
     The gas sensor apparatus according to item 30, wherein the calibration unit is configured to calibrate, based on a highest calibration reliability among the calibration reliabilities of each of the plurality of first gas sensor apparatuses, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 32 
     A gas sensor calibration method comprising: 
     transmitting, by a transmission unit, first calibration information, wherein the first calibration information is calibration information for calibrating a gas concentration in a measurement target which is calculated based on an output of a first gas sensor; 
     receiving, by a reception unit, the first calibration information transmitted in the transmitting; and 
     calibrating, by a calibration unit, based on the first calibration information received in the receiving, a gas concentration in a measurement target which is calculated based on an output of a second gas sensor. 
     Item 33 
     The gas sensor calibration method according to item 32, wherein the measurement target in which the gas concentration is calculated based on the output of the first gas sensor is the same as the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 34 
     The gas sensor calibration method according to item 32 or 33, wherein 
     the second gas sensor is provided in a second gas sensor apparatus, and 
     the second gas sensor apparatus is arranged in an interior space in the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 35 
     The gas sensor calibration method according to item 34, wherein 
     the first gas sensor is provided in a first gas sensor apparatus, 
     the transmitting is further transmitting, by the transmission unit, reliability information indicating a calibration reliability of the first gas sensor apparatus, 
     the receiving is further receiving, by the reception unit, the reliability information transmitted in the transmitting, and 
     the calibrating is calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to the calibration reliability of the first gas sensor apparatus. 
     Item 36 
     The gas sensor calibration method according to item 35, wherein when a reliability of self-calibration of the second gas sensor apparatus is equal to or lower than a predetermined second threshold and also the calibration reliability of the first gas sensor apparatus exceeds a first threshold, the calibrating is calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 37 
     The gas sensor calibration method according to item 35 or 36, wherein the calibrating is comparing, by the calibration unit, the calibration reliability of the first gas sensor apparatus which is received in the receiving with a calibration reliability of the second gas sensor apparatus, and when the calibration reliability of the first gas sensor apparatus is higher than the calibration reliability of the second gas sensor apparatus, calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 38 
     The gas sensor calibration method according to item 36 or 37, further comprising: 
     storing, by a storage unit, the reliability information received in the receiving, wherein 
     the calibrating is comparing, by the calibration unit, the calibration reliability of the first gas sensor apparatus which is received in the receiving with the calibration reliability of the first gas sensor apparatus which is stored in the storing, and when the calibration reliability of the first gas sensor apparatus which is received in the receiving is higher than the calibration reliability stored in the storing, calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 39 
     The gas sensor calibration method according to any one of items 36 to 38, further comprising: 
     acquiring, by a position information acquisition unit, information of a position of the second gas sensor apparatus, wherein 
     the reliability information includes information of a position of the first gas sensor apparatus, and 
     the calibrating is calibrating, by the calibration unit, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to a distance between the position of the first gas sensor apparatus and the position of the second gas sensor apparatus which is acquired in the acquiring. 
     Item 40 
     The gas sensor calibration method according to item 39, wherein when the distance is less than a predetermined distance, the calibrating is calibrating, by the calibration unit, based on the received first calibration information, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 41 
     The gas sensor calibration method according to any one of items 36 to 40, wherein 
     the receiving is receiving, by the reception unit, first calibration information of each of the plurality of first gas sensor apparatuses, and 
     the calibrating is calibrating, by the calibration unit, based on the first calibration information of each of the plurality of first gas sensor apparatuses which is received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 42 
     The gas sensor calibration method according to item 41, wherein 
     the transmitting is further transmitting, by the transmission unit, the reliability information of each of the plurality of first gas sensor apparatuses, 
     the receiving is further receiving, by the reception unit, each of the reliability information transmitted in the transmitting, and 
     the calibrating is applying, by the calibration unit, a weighting to the calibration reliability of each of the plurality of first gas sensor apparatuses, and calibrating, by the calibration unit, based on the calibration reliability to which the weighting has been applied, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 43 
     The gas sensor calibration method according to item 42, wherein the calibrating is calibrating, by the calibration unit, based on a highest calibration reliability among the calibration reliabilities of each of the plurality of first gas sensor apparatuses, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 44 
     A gas sensor calibration method comprising: 
     transmitting, by a transmission unit, first calibration information to a second gas sensor apparatus, wherein 
     the first calibration information is calibration information for calibrating a gas concentration in a measurement target which is calculated based on an output of a first gas sensor. 
     Item 45 
     The gas sensor calibration method according to item 44, wherein 
     the second gas sensor apparatus includes a second gas sensor, and 
     the measurement target in which the gas concentration is calculated based on the output of the first gas sensor is the same as the measurement target in which a gas concentration is calculated based on an output of the second gas sensor. 
     Item 46 
     The gas sensor calibration method according to item 44 or 45, wherein 
     the first gas sensor is provided in a first gas sensor apparatus, and 
     the transmitting is further transmitting, by the transmission unit, reliability information indicating a calibration reliability of the first gas sensor apparatus to the second gas sensor apparatus. 
     Item 47 
     A gas sensor calibration method comprising: 
     receiving, by a reception unit, first calibration information of a first gas sensor apparatus; and 
     calibrating, by a calibration unit, based on the first calibration information received by the reception unit, a gas concentration in a measurement target which is calculated based on an output of a second gas sensor. 
     Item 48 
     The gas sensor calibration method according to item 47, wherein 
     the first gas sensor apparatus includes a first gas sensor, and 
     a measurement target in which a gas concentration is calculated based on an output of the first gas sensor is the same as the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 49 
     The gas sensor calibration method according to item 47 or 48, wherein the second gas sensor is arranged in an interior space in the measurement target in which the gas concentration is calculated based on the output of the second gas sensor. 
     Item 50 
     The gas sensor calibration method according to any one of items 47 to 49, wherein 
     the receiving is further receiving, by the reception unit, reliability information indicating a calibration reliability of the first gas sensor apparatus, and 
     the calibrating is calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to the calibration reliability of the first gas sensor apparatus. 
     Item 51 
     The gas sensor calibration method according to item 50, wherein 
     the second gas sensor is provided in a second gas sensor apparatus, and 
     when a reliability of self-calibration of the second gas sensor apparatus is equal to or lower than a predetermined second threshold and also the calibration reliability of the first gas sensor apparatus exceeds a first threshold, the calibrating is calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 52 
     The gas sensor calibration method according to item 51, wherein the calibrating is comparing, by the calibration unit, the calibration reliability of the first gas sensor apparatus which is received in the receiving with a calibration reliability of the second gas sensor apparatus, and when the calibration reliability of the first gas sensor apparatus is higher than the calibration reliability of the second gas sensor apparatus, calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 53 
     The gas sensor calibration method according to item 51 or 52, further comprising: 
     storing, by a storage unit, the reliability information received in the receiving, wherein 
     the calibrating is comparing, by the calibration unit, the calibration reliability of the first gas sensor apparatus which is received in the receiving with the calibration reliability of the first gas sensor apparatus which is stored in the storing, and when the calibration reliability of the first gas sensor apparatus which is received in the receiving is higher than the calibration reliability stored in the storing, calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 54 
     The gas sensor calibration method according to any one of items 51 to 53, further comprising: 
     acquiring, by a position information acquisition unit, information of a position of the second gas sensor apparatus, wherein 
     the reliability information includes information of a position of the first gas sensor apparatus, and 
     the calibrating is calibrating, by the calibration unit, based on the first calibration information received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor according to a distance between the position of the first gas sensor apparatus and the position of the second gas sensor apparatus which is acquired in the acquiring. 
     Item 55 
     The gas sensor calibration method according to item 54, wherein when the distance is less than a predetermined distance, the calibrating is calibrating, by the calibration unit, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 56 
     The gas sensor calibration method according to any one of items 50 to 55, wherein 
     the receiving is receiving, by the reception unit, the first calibration information of each of the plurality of first gas sensor apparatuses, and 
     the calibrating is calibrating, by the calibration unit, based on the first calibration information of each of the plurality of first gas sensor apparatuses which is received in the receiving, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 57 
     The gas sensor calibration method according to item 56, wherein 
     the receiving is further receiving, by the reception unit, reliability information of each of the plurality of first gas sensor apparatuses, and 
     the calibrating is applying, by the calibration unit, a weighting to the calibration reliability of each of the plurality of first gas sensor apparatuses, and calibrating, by the calibration unit, based on the calibration reliability to which the weighting has been applied, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 58 
     The gas sensor calibration method according to item 53, wherein the calibrating is calibrating, by the calibration unit, based on a highest calibration reliability among the calibration reliabilities of each of the plurality of first gas sensor apparatuses, the gas concentration in the measurement target which is calculated based on the output of the second gas sensor. 
     Item 59 
     A gas sensor calibration program for causing a computer to execute the gas sensor calibration method according to any one of items 32 to 43. 
     Item 60 
     A gas sensor calibration program for causing a computer to execute the gas sensor calibration method according to any one of items 44 to 46. 
     Item 61 
     A gas sensor calibration program for causing a computer to execute the gas sensor calibration method according to any one of items 47 to 58. 
     EXPLANATION OF REFERENCES 
       10 : reception unit,  11 : first gas sensor,  12 : display unit,  13 : transmission unit,  14 : calibration unit,  15 : control unit,  16 : position information acquisition unit,  20 : reception unit,  21 : second gas sensor,  22 : display unit,  23 : transmission unit,  24 : calibration unit,  25 : control unit,  26 : position information acquisition unit,  30 : reception unit,  31 : third gas sensor,  32 : display unit,  33 : transmission unit,  34 : calibration unit,  35 : control unit,  90 : living body,  100 : first gas sensor apparatus,  110 : computation unit,  112 : storage unit,  114 : AD conversion unit,  120 : computation unit,  122 : storage unit,  124 : AD conversion unit,  150 : gas sensor apparatus,  200 : second gas sensor apparatus,  250 : gas sensor apparatus,  300 : third gas sensor apparatus,  400 : gas sensor system,  501 : measurement target,  502 : measurement target,  503 : gas,  504 : gas,  505 : measurement target,  508 : interior space,  600 : gas sensor,  2200 : computer,  2201 : DVD-ROM,  2210 : host controller,  2212 : CPU,  2214 : RAM,  2216 : graphics controller,  2218 : display device,  2220 : input and output controller,  2222 : communication interface,  2224 : hard disk drive,  2226 : DVD-ROM drive,  2230 : ROM,  2240 : input and output chip,  2242 : keyboard.