System for collecting lung function data, the system comprising a mobile hand-held spirometer for measuring lung function and providing lung function data; a mobile hand-held computer comprising a processor, a memory, a clock, and a screen; and wherein the spirometer and the mobile hand-held computer are separate devices, the spirometer and the mobile hand-held computer are configured to communicate electronically with each other; wherein the processor is configured for collecting the measured lung function data from the spirometer via the electronic communication between the spirometer and the mobile hand-held computer, and storing the lung function data in the memory; characterized in that the processor is further configured for collecting, with the system, lung function data from the spirometer by indicating on the screen of, and/or sound from, the mobile hand-held computer to use the spirometer only when A) or B) occurs, wherein the configuration of the processor includes A) and B), and A) and B) comprises: A) when the clock reaches a predetermined recurring time within 24 hours, with at least 10 hours between, and B) before and after the mobile hand-held computer indicates to take any lung medication, or after the mobile hand-held computer indicates that any lung medication has been taken; calculating, by the processor, a variation between all collected lung function data stored in the memory, the variation is the coefficient of variation expressed in percentage; repeating the indication to use the spirometer only when A) or B) occur and repeating the calculation of the variation; and stopping the system to collect measurements from the spirometer or indicating on the screen to stop using the spirometer, when the processor compares the variation between all collected lung function data is more than 20 percent or after a maximum of collecting lung function data for 14 days. a mobile hand-held spirometer for measuring lung function and providing lung function data; a mobile hand-held computer comprising a processor, a memory, a clock, and a screen; and wherein the spirometer and the mobile hand-held computer are separate devices, the spirometer and the mobile hand-held computer are configured to communicate electronically with each other; wherein the processor is configured for collecting the measured lung function data from the spirometer via the electronic communication between the spirometer and the mobile hand-held computer, and storing the lung function data in the memory; characterized in that the processor is further configured for collecting, with the system, lung function data from the spirometer by indicating on the screen of, and/or sound from, the mobile hand-held computer to use the spirometer only when A) or B) occurs, wherein the configuration of the processor includes A) and B), and A) and B) comprises: A) when the clock reaches a predetermined recurring time within 24 hours, with at least 10 hours between, and B) before and after the mobile hand-held computer indicates to take any lung medication, or after the mobile hand-held computer indicates that any lung medication has been taken; A) when the clock reaches a predetermined recurring time within 24 hours, with at least 10 hours between, and B) before and after the mobile hand-held computer indicates to take any lung medication, or after the mobile hand-held computer indicates that any lung medication has been taken; calculating, by the processor, a variation between all collected lung function data stored in the memory, the variation is the coefficient of variation expressed in percentage; repeating the indication to use the spirometer only when A) or B) occur and repeating the calculation of the variation; and stopping the system to collect measurements from the spirometer or indicating on the screen to stop using the spirometer, when the processor compares the variation between all collected lung function data is more than 20 percent or after a maximum of collecting lung function data for 14 days.