Abstract:
A method and apparatus involve: providing a plurality of products that are each associated with a respective radio frequency identification tag; using radio frequency identification technology to automatically identify specific products in a group of products collected by a shopper; and evaluating whether or not to obtain payment from the shopper based on the radio frequency identification of products in the group. Based on the result of the evaluation, either payment is obtained from the shopper on the basis of the radio frequency identification of products in the group, or else the products in the group are audited, and then payment is obtained on the basis of the products identified by the audit.

Description:
[0001]    This application is a continuation of U.S. application Ser. No. 12/267,068 filed Nov. 7, 2008, which claims the priority under 35 U.S.C. §119 of provisional application No. 60/996,262 filed Nov. 8, 2007, the disclosure of both of which are hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to techniques for shopper checkout and, more particularly, to techniques that facilitate efficient checkout of a shopper. cl BACKGROUND 
         [0003]    Shopper checkout is the process of identifying all of the products selected by a shopper, and then obtaining payment from the shopper for those products. Retail stores typically use two different techniques for shopper checkout. First, in the most common approach, a clerk employed by the store manually passes each product selected by the shopper past a universal product code (UPC) scanner, and the scanner reads the UPC code on each product. The UPC scanner is coupled to a computer, and the computer uses the scanned UPC code from each product to retrieve from a stored product list an identification of the product, and also the price of the product. The computer sums the individual prices of all products scanned in order to obtain a subtotal, and then adds any applicable taxes or other charges to the subtotal, thereby obtaining the total amount owed by the shopper. The clerk then obtains payment of that total amount from the shopper in order to complete the checkout process. 
         [0004]    The other common approach is self-service checkout. During self-service checkout, it is the shopper rather than a store clerk who manually scans the UPC code on each product. A single clerk is typically present to monitor four or more self-service checkout stations, and to deal with any questions or problems encountered by shoppers operating the self-service checkout stations. The self-service approach is significantly less expensive for the store, because the store pays wages and benefits only for the single clerk who monitors several self-service checkout stations, instead of paying wages and benefits for several clerks who are each located at a respective different checkout station. On the other hand, the self-service approach has some drawbacks. For example, a shopper may inadvertently or intentionally fail to scan the UPC code on one or more products, such that the computer calculating the total amount due is not aware of those products and thus omits their prices from the total. As a result, the shopper ends up taking home one or more products that the shopper did not pay for. 
         [0005]    While these traditional approaches have each been generally adequate for their intended purposes, they each have some drawbacks, and neither has been entirely satisfactory in all respects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  is a diagrammatic fragmentary sectional top view of a portion of a retail store, and in particular shows a portion of the store where shoppers check out and pay for their purchases. 
           [0008]      FIG. 2  is a diagrammatic fragmentary side view showing in an enlarged scale an interrogation zone present in the portion of the store depicted in  FIG. 1 , and also showing a shopper and a shopping cart that are in the interrogation zone. 
           [0009]      FIG. 3  is a block diagram of a control system that includes several electronic components shown in  FIGS. 1 and 2 , as well as a central computer system that is operatively coupled to each of these electronic components. 
           [0010]      FIG. 4  is a diagrammatic view of a master product list that is stored in a memory of the computer system of  FIG. 3 . 
           [0011]      FIGS. 5A and 5B  are a flowchart showing a procedure that is part of the processing carried out by the computer system of  FIG. 3 . 
           [0012]      FIGS. 6 and 7  show respective tables of information that are each stored in the memory of the computer system of  FIG. 3 , and that are used by the procedure of  FIGS. 5A and 5B . 
           [0013]      FIG. 8  is a flowchart showing a procedure that is an alternative embodiment of the procedure shown in  FIGS. 5A and 5B . 
           [0014]      FIGS. 9 and 10  show respective tables of information that can be substituted for the table of  FIG. 6 , and used by the procedure of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  is a diagrammatic fragmentary sectional top view of a portion  10  of a retail store, and in particular shows the portion of the store where shopper checkout occurs. Shopper checkout is the process of identifying all of the products selected by a shopper, and then obtaining payment from the shopper for those products. 
         [0016]    The portion  10  of the store includes a corridor or passage  12  that splits into two corridors or passages  13  and  14 , each of which leads to a respective one of two checkout areas  17  and  18  that are partially separated by a wall  21 . The corridors  13  and  14  each open into the associated checkout area  17  or  18  on one side thereof, and a single exit door  22  is provided on the opposite side thereof to permit shoppers to exit the store after completing the checkout process. 
         [0017]    The checkout area  17  has three checkout stations  31 ,  32  and  33 , and the checkout area  18  has three checkout stations  34 ,  35  and  36 . Each of the checkout stations  31 - 36  includes a respective point-of-sale (POS) terminal  41 - 46  that is an electronic cash register of a known type. In  FIG. 1 , the checkout stations  31 - 36  are each manned by a respective person  51 - 56  who is a store clerk. In an alternative configuration, the three POS terminals  41 - 43  in the checkout area  17  could be replaced with self-service POS terminals of a type well known in the art. In the case of self-service POS terminals, a single store clerk might be stationed nearby to monitor all three checkout stations  41 - 43 , or the store might elect to provide no store clerk in the checkout area  17 . 
         [0018]    Shoppers who are waiting to check out proceed in single file down the corridor  12 . For example,  FIG. 1  shows three shoppers  61 - 63  in the corridor  12 , each with a respective shopping cart  64 ,  65  or  66 . An interrogation zone  68  is provided at the end of corridor  12  nearest the corridors  13  and  14 . The interrogation zone is discussed in more detail later. In  FIG. 1  the shopper  63  with the cart  66  is currently located in the interrogation zone  68 . 
         [0019]    In  FIG. 1 , an electronic display  69  is provided at the intersection of the corridors  13  and  14 . Depending on what happens in the interrogation zone  68 , the display  69  will illuminate either an arrow pointing to the left or an arrow pointing to the right, in order to indicate to the shopper in the interrogation zone that he or she should proceed down either the corridor  13  or the corridor  14 .  FIG. 1  shows two shoppers  71  and  72  with respective carts  73  and  74  who were directed to proceed down the corridor  13  to the checkout area  17 , and who are currently in the process of checking out.  FIG. 1  also shows a shopper  77  with a cart  78  who was directed to proceed down the corridor  14  to the checkout area  18 , and who is currently in the process of checking out. 
         [0020]      FIG. 2  is a diagrammatic fragmentary side view showing in an enlarged scale the interrogation zone  68  of  FIG. 1 , and also showing the shopper  63  and shopping cart  66  in the interrogation zone. The shopping cart  66  contains several products  101 - 104  that the shopper  63  selected and intends to purchase. Although  FIG. 2  shows four products  101 - 104 , the cart  66  could alternatively include a larger or smaller number of products. Each of the products  101 - 104  has a respective radio frequency identification (RFID) tag  106 - 109  mounted thereon. The tags  106 - 109  are each a type of device well known in the art, and are therefore not illustrated and described here in detail. A child  113  is sitting in the shopping cart. The shopper  63  may also have one or more personal effects in the cart, such as a purse. 
         [0021]    In  FIG. 2 , the shopping cart  66  is resting on a scale  116  of a known type, which weighs the cart  66  and everything in the cart, and then outputs an electrical signal representing the total measured weight. A digital camera  118  of a known type is stationarily supported above the scale  116 . Although  FIG. 2  shows only one camera  118 , it would alternatively be possible to have two or more cameras that view the cart and its contents from different angles. The camera  118  records one or more images of the cart and its contents as the cart passes below the camera. The camera  118  then outputs these images in the form of electrical signals. The images from the camera  118  are then processed with image processing software in an effort to identify items present in the shopping cart  66 , including the number of products  101 - 104 , any child  113 , and any personal effects such as a purse. The camera  118  in  FIG. 2  is responsive to visual light, and the recorded images are digital photographs. Alternatively, however, the camera  118  could be responsive to radiation in a waveband other than visible light, such as infrared radiation, or low-level x-ray radiation. 
         [0022]    As the shopper  63  continues to push the cart  66  in a forward direction, the cart  66  will pass between two RFID readers  121  and  122 . The readers  121  and  122  are each a device of a well-known type, and are therefore not illustrated and described here in detail. The reader  121  is stationarily supported above the cart&#39;s path of travel, and the reader  122  is embedded in the floor below the cart&#39;s path of travel. Although  FIG. 2  shows two readers  121  and  122 , it would alternatively be possible to have a larger or smaller number of readers. Also,  FIG. 2  shows the readers  121  and  122  located respectively above and below the path of travel of the cart, but it would alternatively be possible to provide the readers  121  and  122  in other locations. For example, the readers  121  and  122  could be provided on opposite sides of the path of travel of the shopping cart  66 . 
         [0023]    The readers  121  and  122  in  FIG. 2  emit RFID signals of a known type. As the shopping cart  66  passes between the readers  121  and  122 , the signals emitted by the readers will reach most or all of the tags  106 - 109 . Each tag that receives a signal from either reader will produce in reply an RFID signal containing an identification code. The signal emitted by each tag will then be received by one or both of the readers  121  and  122 . The identification code in each received signal can be used to identify the tag that emitted the signal, and thus identify the particular product associated with that tag. 
         [0024]    In theory, all of the tags will receive the interrogation signals from the readers, such that all of the tags will produce a signal in reply, and all of the signals from the tags will be received by the readers. But as a practical matter, some types of products make it more difficult to scan tags than other types of products. For example, if a product includes a significant amount of metal, the metal can provide a degree of electromagnetic shielding that interferes with attempts to communicate with the tag on that metal product, and/or with tags on other products located near the metal product. Similarly, if a product contains a significant amount of water, that may make it more difficult to communicate with the tag on that product, and/or with tags on other nearby products. As a result, the readers  121  and  122  may not always be able to accurately identify each and every product present in the shopping cart  66 . A further consideration is that the readers  121  and  122  cannot identify items in the shopping cart that do not have RFID tags, such as the child  113 , or personal effects of the shopper, such as a purse. 
         [0025]      FIG. 3  is a block diagram of a control system  151  that includes several electronic components discussed above in association with  FIGS. 1 and 2 , as well as a central computer system  152  that is operatively coupled to each of these electronic components. More specifically,  FIG. 3  shows the POS terminals  41 - 46  and the display  69  of  FIG. 1 , each of which is electrically coupled to the central computer system  152 . In addition,  FIG. 3  shows the scale  116 , camera  118  and readers  121 - 122  of  FIG. 2 , each of which is electrically coupled to the central computer system  152 .  FIG. 3  does not show everything in the control system  151  or in the computer system  152 , but instead only shows selected portions thereof that facilitate an understanding of the present invention. 
         [0026]      FIG. 3  shows a master terminal  156  that is electrically coupled to the central computer system  152 . The master terminal  156  and the central computer system  152  are not visible in  FIGS. 1 and 2 , because they are located in the business office of the illustrated store, where they can be accessed by store management but not shoppers. Store management can provide the master terminal  156  with a password, and then use the master terminal to adjust data within the central computer system  152 . In the disclosed embodiment, the central computer system  152  includes computer hardware in the form of a conventional, commercially-available computer of the type commonly known as a personal computer. For example, the hardware of the computer system  152  could be a standard personal computer obtained commercially from Dell, Inc. of Round Rock, Tex. Alternatively, however, the hardware of the computer system  152  could be any other suitable computer hardware. 
         [0027]    The computer system  152  includes a processor  161  and a memory  162 . The processor  161  is a microprocessor of a known type, and is therefore not described here in detail. The memory  162  is a diagrammatic representation of the storage available within the central computer system  152 , and may include more one than one type of memory. For example, the memory  162  may include one or more of a read only memory (ROM), a random access memory (RAM), a flash memory, a hard disc drive, or any other suitable type of memory. 
         [0028]      FIG. 3  diagrammatically shows some of the information that is maintained within the memory  162 . More specifically, the memory  162  stores a software program  166  that is executed by the processor  161 . A portion of the program  166  is image processing software  167 . As mentioned earlier, the image processing software  167  accepts digital images produced by the camera  118 , and analyzes these images in an effort to identify the cart and items disposed in the cart, such as the products  101 - 104  ( FIG. 2 ), any child  113 , and/or any personal effects such as a purse. 
         [0029]    The memory  162  also stores several segments of cart data, three of which are shown at  171 ,  172  and  173 . Each segment of cart data  171 - 173  is created as a respective shopping cart passes through the interrogation zone  68 , contains information derived from that cart in the interrogation zone  68 , and is maintained in the memory  162  until checkout of that particular cart has been completed. The segments of cart data  171 ,  172  and  173  are all similar, and therefore only the segment  171  is shown and described in detail. 
         [0030]    More specifically, the segment of cart data  171  includes a measured cart weight  176 , which is the total weight of the particular cart and its contents, as measured by the scale  116  in the interrogation zone. The cart data segment  171  also includes an RFID tag count  177 , which is the number of RFID tags detected in that cart by the readers  121  and  122 . The cart data  171  further includes an RFID product list  178 . As discussed above, the RFID tag on each product produces a wireless signal containing a code that is used to identify the particular product on which that tag is mounted. The RFID product list  178  is a list of all products identified in the cart through communication with RFID tags on the products. The cart data segment  171  also includes an actual product count  179 , which is the number of separate products detected by the image processing software  167 , based on the images produced by the camera  118 . 
         [0031]    The memory  162  stores a cart tare weight value  182 , which is the predetermined weight of the shopping cart  66  when it is empty. 
         [0032]    As discussed above, some products make it more difficult to read RFID tags than other products. Consequently, it is possible for the RFID readers  121  and  122  to miss one or more products in a cart. Similarly, the camera  118  produces images that are analyzed in an effort to identify each of the products in the cart. However, the image processing software  167  may not be able to accurately identify each and every product in the cart. For example, a small product may be located beneath some larger products in the cart, and thus may not be visible in any of the images from the camera  118 . Consequently, for any given shopping cart, product lists generated from information obtained in the interrogation zone  68  using RFID technology or imaging technology may or may not include all of the products actually present in the cart. 
         [0033]    The store may elect to permit a shopper to check out based solely on a product list generated from information obtained in the interrogation zone  68 . However, if that list is incomplete, the shopper would take home one or more products that the shopper did not pay for. This is commonly referred to as shrinkage of the store&#39;s inventory. 
         [0034]    On any given day (or during certain periods of the day), a store may not be very busy, and this or other circumstances may make the store unwilling to accept much shrinkage. Accordingly, instead of checking out all carts based on product list(s) generated from information obtained in the interrogation zone  68 , the store may prefer to select a subset of the carts that are checking out, and perform a double-check or audit of the products actually present in each of those carts, in order to generate a very accurate product list for each such cart that is then used for checkout. On the other hand, on any given day (or during certain periods of the day), the store may be very busy and may have a long line of shoppers waiting to check out, and this or other circumstances may make the store more willing to accept a higher risk of shrinkage, in order to keep shoppers happy by checking them out more rapidly. Accordingly, the store may subject fewer carts (or no carts) to a double-check or audit. 
         [0035]    In  FIG. 3 , the memory  162  of the computer system  152  stores a business value  183 . The business value  183  can be set by store management using the master terminal  156 , and specifies the store&#39;s current willingness to tolerate shrinkage. More specifically, the business value  183  is an integer number between 1 and 10, inclusive. The values of 1 to 10 represent a sliding scale of tolerance for shrinkage, where 1 represents the maximum tolerance for shrinkage with the smallest percentage of carts being double-checked or audited, and 10 represents the least tolerance for shrinkage with a substantially higher percentage of carts being double-checked or audited. 
         [0036]    The business value  183  influences the determination of whether each shopper in the corridor  12  ( FIG. 1 ) will be directed to proceed down the corridor  13  or down the corridor  14 , in a manner discussed in more detail later. Carts that are directed down the corridor  13  end up in the checkout area  17 , where checkout is completed using the RFID product list  177  generated from information obtained using RFID technology in the interrogation zone  68 . In contrast, carts that are directed to proceed down the corridor  14  end up in the checkout area  18 , where a double-check or audit is carried out on each such cart, and then checkout is completed based on the results of the double-check or audit. For example, in the checkout area  18 , one of the clerks  54 - 56  may use a standard UPC scanner to manually scan the universal product code (UPC) on each product in a cart, in order to generate a highly accurate product list that is then used for checkout. 
         [0037]    The memory  162  stores a set of weighting values  184 . In the disclosed embodiment, there are six weighting values W 1 , W 2 , W 3 , W 4 , W 5  and W 6 , each of which is an integer value between 1 and 5 inclusive, where 5 represents the greatest weight, and 1 represents the least weight. The weighting values  184  can each be adjusted by store management through the master terminal  156 . The memory  162  also stores a default threshold  186 . In the disclosed embodiment, the default threshold is a single integer between 0 and 100 inclusive, and represents a percentage, such as 65%. The default threshold  186  can be adjusted by store management through the master terminal  156 . 
         [0038]    The memory  162  also stores a master product list  188 .  FIG. 4  is a diagrammatic view of the master product list  188 . The master product list  188  is shown in  FIG. 4  as a table, with a separate row for each type of product carried by the store. Each row has the same set of fields, and some of these fields are depicted in the first row in  FIG. 4 . In particular, for each product or row, there is a field  191  setting forth the name of the product, a field  192  setting forth the industry-standard UPC code for that product, a field  193  setting forth the price charged by the store for that product, a field  194  setting forth the weight of the product, and a field  195  setting forth a difficulty rating. 
         [0039]    Each difficulty rating  195  is an integer number between 1 and 10, inclusive. As discussed above, some types of products (such as those that contain metal or water) are more likely to interfere with the scanning of RFID tags than other types of products. The numerical difficulty rating in the field  195  is an indication of the extent to which the associated product is likely to interfere with scanning of the RFID tag mounted on that product, or RFID tags on other nearby products. A value of 1 represents the least degree of interference or difficulty, and a value of 10 represents the greatest degree of interference or difficulty. Store management can use the master terminal  156  to change the information in the master product list  188 , including the difficulty ratings  195 . For simplicity,  FIG. 4  shows the difficulty ratings  195  as an integral portion of the master product list  188 . However, the difficulty ratings  195  could alternatively be maintained in a separate list. 
         [0040]    Referring again to  FIG. 3 , the memory  162  in the central computer system  152  also stores several tables  197 , each of which is discussed in more detail later. 
         [0041]      FIGS. 5A and 5B  are a flowchart showing a procedure that is a portion of the processing carried out by the processor  161  under control of the program  166 . The flowchart of  FIGS. 5A and 5B  shows how the processor  161  decides whether to direct a shopper along either the corridor  13  or the corridor  14 . More specifically, as soon as a given shopping cart has been interrogated in the interrogation zone  68  ( FIGS. 1 and 2 ), the processor  161  carries out an evaluation that is based primarily on data collected during the interrogation. Then, the processor makes a decision about whether to direct the cart along the corridor  13  to the checkout area  17 , or along the corridor  14  to the checkout area  18 . As discussed above, in the checkout area  17  shoppers check out and pay based on the product list compiled using RFID technology. In contrast, in the checkout area  18 , the products in each cart are audited (for example by scanning UPC codes), in order to generate a new and accurate product list that is then used for checkout. 
         [0042]    As discussed in more detail below, the procedure of  FIGS. 5A and 5B  involves successive evaluation of six different criteria. Each criteria looks for a respective different condition that suggests a likelihood the RFID product list  178  might not be fully accurate. If the cart fails to meet any one of these six criteria, then the contents of the cart are audited in the checkout area  18 . On the other hand, if the cart meets all six criteria, then the cart is sent to checkout area  17 , and is not audited. 
         [0043]    In more detail, the routine of  FIGS. 5A and 5B  is entered at block  211 , and then control proceeds to block  212 . In block  212 , the processor  161  prepares a filtered product list. In this regard,  FIG. 6  shows a table that is one of the tables stored at  197  ( FIG. 3 ) in the memory  162 , and that has six columns  216 - 221 . The left column  216  sets forth each possible value of the business value stored at  183  in the memory  162  ( FIG. 3 ), and the adjacent column  217  shows a corresponding difficulty threshold. In the disclosed embodiment, the difficulty threshold happens to be the same as the business value. For example, if the business value is currently 1 then the difficulty threshold is 1, and if the business value is 5 then the difficulty threshold is 5. The processor uses columns  216  and  217  to identify the difficulty threshold associated with the current value of the business value  183 . 
         [0044]    The processor then identifies each product from the master product list  188  that currently has a difficulty rating ( 195  in  FIG. 4 ) exceeding the current difficulty threshold obtained from column  217 . These products collectively constitute the filtered product list. The processor then compares this filtered product list to the RFID product list  178  ( FIG. 3 ) for the shopping cart that has just been interrogated. Basically, the processor is looking for products (if any) that are on both lists. Any product present on both lists will have a difficulty rating that suggests the product might have blocked access to one or more RFID tags, such that one or more products actually present within the cart may not appear on the RFID product list. In  FIG. 5A , control proceeds to block  226 , where the processor checks to see whether the comparison yielded any matches, or in other words whether any product was on both lists. If any product is on both lists, then the RFID product list may not be accurate, and control proceeds to block  227 . 
         [0045]    In block  227 , the processor causes the display  69  in  FIG. 1  to illuminate an arrow pointing to the right, indicating to the shopper in the interrogation zone  68  that he or she should proceed down the corridor  14  to the checkout area  18 . In the checkout area  18 , the products in the cart will be carefully audited (for example by having a store clerk manually scan the UPC code on each product). Checkout will then be completed using the product list from the audit. From block  227 , the processor proceeds to block  228 , and exits the routine of  FIG. 5B . 
         [0046]    Referring back to block  226 , if it was determined that that there was no match, or in other words that no product on the RFID product list was also on the filtered product list, then control proceeds to block  231 . In block  231 , the processor  161  takes the RFID tag count  177  ( FIG. 3 ), and compares it to a tag count threshold. More specifically, with reference to  FIG. 6 , the processor locates the current business value in column  216 , and then selects a corresponding tag count threshold from column  218 . In essence, as the number of products in the shopping cart increases (such that the number of RFID tags also increases), it becomes more difficult to accurately identify each and every tag with RFID technology. Stated differently, as the number of products and tags increases, there is a progressively increasing chance that the RFID identification process may have missed one or more of the products in a cart. In block  231 , the processor compares the RFID tag count  177  to the tag count threshold obtained from column  218 . If the tag count exceeds the threshold, then control proceeds to block  227  for an audit of the products in the cart. It will be noted from  FIG. 6 , that, as the business value progressively increases, representing a progressively increasing preference for accuracy at checkout, the tag count threshold in column  218  progressively decreases, meaning that progressively smaller product counts will trigger an audit. 
         [0047]    In block  231 , if the RFID tag count does not exceed the tag count threshold, then control proceeds to block  232 . In block  232 , the processor takes the measured cart weight  176  ( FIG. 3 ), and subtracts the cart tare weight  182  in order to determine the measured product weight, or in other words the total weight of all contents of the cart. Note that this measured product weight will include not only products in the cart, but also anything else in the cart, such as a child  113  ( FIG. 2 ) or personal effects such as a purse. However, to the extent that the image processing software  167  can identify a child and/or personal effects in the cart, it would optionally be possible to subtract a predetermined weight value from the measured product weight calculated in block  232 , in order to at least partially compensate for the child and/or the personal effect. 
         [0048]    From block  232 , control proceeds to block  233 , where the measured product weight calculated in block  232  is compared to a weight threshold. With reference to  FIG. 6 , the processor locates the current value of the business value in column  216 , and then selects a corresponding weight threshold from column  219 . If the measured product weight exceeds this weight threshold, then control proceeds from block  233  to block  227  for an audit of the contents of the cart. In essence, as the weight of products in the cart increases, either the total number of products is increasing, and/or the shopper is purchasing one or more heavier and potentially more valuable products, such as a television. It will be noted from  FIG. 6  that, as the value of the business value in column  16  progressively increases, representing a progressively greater desire for an accurate product list at checkout, the weight threshold in column  219  progressively decreases, meaning that progressively fewer and/or lighter products will trigger an audit. 
         [0049]    If it is determined in block  233  that the measured product weight does not exceed the weight threshold, then control proceeds from block  233  to block  236 . In block  236 , the processor takes the measured product weight determined in block  232 , and checks to see whether this measured product weight and the RFID tag count  177  both fall within a specified window width. In this regard, with reference to  FIG. 6 , the processor locates the current value of the business value in column  216 , and then selects a corresponding window width from column  220 .  FIG. 7  shows a table that is one of the tables stored at  197  ( FIG. 3 ) in the memory  162 , and that has 10 columns or “buckets” each relating a respective range of RFID tag counts to a respective weight range. The window width obtained from column  220  in  FIG. 6  represents a number of adjacent columns in the table of  FIG. 7 . For example, if the window width is 1, then that represents one column in the table of  FIG. 7 , and the tag count and the measured weight should both be within the same column. Reference numeral  241  represents a window width of 1 column in  FIG. 7 . If the RFID tag count is in the range of 21 to 25, then the measured product weight should be in the range of 81 to 100 pounds. The window  241  is a sliding window, and could be associated with any single column in the table of  FIG. 7 , but the tag count and weight both need to be in that same column. 
         [0050]    Alternatively, assume that the window width is 2 columns. Reference numerals  242  and  243  show two different possible positions of a sliding window having a width of two columns. Taking both of the window positions  242  and  243  into account, it will be noted that if the RFID tag count is in the range of 21 to 25, then the measured weight needs to be somewhere within the three columns spanned by the two window positions  242  and  243 , or in other words in the range of 61 to 120 pounds. As still another example, reference numerals  244 ,  245  and  246  show three different positions of a sliding window having a width of 3 columns. Taking all three window positions  244 ,  245  and  246  into account, it will be noted that if the RFID tag count is in the range of 21 to 25, then the measured weight would need to be in the range of 41 to 140 pounds. 
         [0051]    These are examples of how the processor  161  determines in block  236  ( FIG. 5A ) whether the measured product weight and the RFID tag count are both within the current window width. If they are not both within the window width, then control proceeds to block  227  for an audit of the contents of the cart. In essence, most shopping carts will exhibit a relatively close correlation between the number of tags read and the measured weight of the products. But if there is a differential that exceeds a specified tolerance (the current window width), then it raises a question as to whether the RFID product was accurate, and thus an audit is appropriate. 
         [0052]    If it is determined in block  236  that the measured product weight and the RFID tag count are both within the appropriate window width, then control proceeds to block  251 . In block  251 , the processor takes the RFID product list  178 , and looks up each listed product in the master product list  188 , in order to determine the actual weight  194  ( FIG. 4 ) of that particular product. The processor then adds up all of these weights in order to calculate the total weight of the products in the cart (as based on the information obtained using RFID technology). Then, the processor subtracts from the calculated product weight determined in block  251  the measured product weight determined in block  232  (which is based on the measurement made with scale  116 ). The processor takes the absolute value of the difference, in order to obtain a weight differential that is a positive number. 
         [0053]    The measured product weight and the calculated product weight should usually be approximately the same. In other words, the calculated weight differential should usually be relatively small. The larger the weight differential, the greater the likelihood that the RFID product list may not include all of the products actually present in the cart, and thus the greater the justification for auditing the products in the cart. Accordingly, in block  252 , the weight differential calculated in block  251  is compared to a differential threshold. In this regard, with reference to  FIG. 6 , the processor locates the current value of the business value  183  in column  216 , and then selects a corresponding differential threshold from column  221 . It will noted that, as the business value progressively increases, representing a progressively greater desire for accuracy in the product list used for checkout, the differential threshold in column  221  progressively decreases, such that progressively smaller weight differentials will trigger an audit of the contents of the cart. In block  252 , if the calculated weight differential exceeds the differential threshold obtained from column  221 , control proceeds to block  227  for an audit of the contents of the cart. 
         [0054]    If it is determined in block  252  that the calculated weight differential does not exceed the specified differential threshold, then control proceeds to block  253 . In block  253 , the actual product count obtained by analyzing images from the cameral  118  is compared to the RFID product count obtained by interrogating RFID tags on products in the cart (or in other words the total number of products in the RFID product list  178  in  FIG. 3 ). If these two product counts do not match exactly, then it suggests the RFID product list might not be entirely accurate, and so control proceeds to block  227  in order to carry out an audit of the contents of the cart. Otherwise, control proceeds from block  253  to block  254 . 
         [0055]    In block  254 , the processor causes the display  69  in  FIG. 1  to illuminate an arrow pointing to the left, indicating that the shopper in the interrogation zone  68  should proceed down the corridor  13  to the checkout area  17 , where checkout and payment will be carried out using the RFID product list  178 . Control then proceeds to block  228 , for an exit from the routine of  FIG. 5B . 
         [0056]      FIG. 8  is a flowchart showing a procedure that is an alternative embodiment of the procedure shown in  FIGS. 5A and 5B . In  FIGS. 5A and 5B , the procedure is influenced by the current state of the business value  183  ( FIG. 3 ), as explained in more detail above. In contrast,  FIG. 8  takes a different approach that does not involve use of the business value  183 . In particular, as discussed in more detail below, the procedure of  FIG. 8  successively evaluates six different criteria that are similar to the six criteria used in the procedure of  FIGS. 5A and 5B . The check of each criteria results in the determination of a respective confidence level for that criteria, where the confidence level is expressed as a percentage. The six confidence levels are then weighted, and combined to arrive at an overall confidence level. If the overall confidence level is above a threshold, then the cart is directed to checkout area  17 , where checkout is carried out using the RFID product list  178 . On the other hand, if the overall confidence level is below the threshold, then the cart is directed to checkout area  18 , where an audit is performed, and checkout is carried out using the product list from the audit. 
         [0057]    Turning now in more detail to  FIG. 8 , processing begins at  301 , and proceeds to block  302 . In block  302 , the processor  161  takes the RFID product list  178  ( FIG. 3 ), and looks each listed product up in the master product list  188  ( FIGS. 3 and 4 ), in order to obtain the current difficulty rating  195  for that product. The processor then adds up all these difficulty ratings, and divides the sum by the number of products in the RFID product list, in order to obtain an average of the difficulty ratings for all products in the RFID product list  178 . The average will necessarily be a number between 1 and 10. The processor multiplies this average by 10, in order obtain a percentage, and then subtracts this percentage from 100% in order to obtain a first percentage “%1”. 
         [0058]    Control then proceeds from block  302  to block  303 . In block  303 , the processor uses the RFID tag count  177  to determine a second percentage “%2”. More specifically,  FIG. 9  is a table that is one of the tables stored at  197  ( FIG. 3 ) in the memory  162 , and that has four columns  306 ,  307 ,  308  and  309 . The left column  306  lists different possible values for the RFID tag count, and the right column  309  gives corresponding confidence levels, each expressed as a respective different percentage. The processor looks the RFID tag count  177  up in the left column  306 , and then selects the associated percentage from column  309 , for use as the second percentage “%2”. 
         [0059]    The processor then proceeds from block  303  to block  311 . In block  311 , the processor calculates a measured product weight in the same manner already discussed above in association with block  232  in  FIG. 5A . The processor looks this measured product weight up in column  307  of the table in  FIG. 9 , and then selects the corresponding percentage from the right column  309  for use as a third percentage “%3”. 
         [0060]    The processor then proceeds from block  311  to block  312 . In block  312 , the processor determines a forth percentage “%4” based on the RFID tag count  177  ( FIG. 3 ), and the measured product weight calculated in block  311 . More specifically, with reference to  FIG. 7 , the processor identifies the column in  FIG. 7  that corresponds to the RFID tag count  177 , and also identifies the column that contains the measured product weight. If they are both in the same column, then the number of columns spanned is 1. If they are not in the same column but are in adjacent columns, then the number of columns spanned is 2. Similarly, if they are in different columns that have a single further column between them, then the number of column spanned is three. In this manner, the processor thus determines the number of columns in  FIG. 3  that are spanned by the RFID tag count and the measured product weight. 
         [0061]      FIG. 10  is a table that is one of the tables stored at  197  ( FIG. 3 ) in the memory  162 . The left column  316  contains possible values for the number of columns spanned in  FIG. 7 , and the right column  317  contains respective confidence levels, each expressed as a percentage. After determining the number of columns spanned in  FIG. 7 , the processor looks this number up in the left column  316  of the table in  FIG. 10 , and then selects the corresponding percentage from column  317  to serve as the fourth percentage “%4”. 
         [0062]    The processor then proceeds from block  312  to block  321 . In block  321 , the processor uses the RFID product list  178  and the master product list  188  ( FIG. 3 ) to calculate a weight differential, in the same manner discussed above in association with block  251  of  FIG. 5B . The processor looks this weight differential up in column  308  of the table in  FIG. 9 , and then selects the corresponding percentage from column  309  for use as a fifth percentage “%5”. 
         [0063]    The processor then proceeds to block  322 , where it compares the actual product count  179  ( FIG. 3 ) to the RFID product count, which is the number of products present in the RFID product list  178 . This is equivalent to the comparison that was already discussed above in association with block  253  of  FIG. 5B . If the actual product count is exactly the same as the RFID product count, then the processor proceeds to block  323 , where it sets a sixth percentage “%6” to be 100%. Alternatively, if the actual product count and RFID product count are found to be different in block  322 , then the processor proceeds to block  324 , where it sets the sixth percentage “%6” to be 0%. From either of blocks  323  or  324 , the processor proceeds to block  326 . 
         [0064]    As discussed above in association with  FIG. 3 , the memory  162  contains weighting values  184 , and in particular six weighting values W 1 , W 2 , W 3 , W 4 , W 5  and W 6  that are each an integer between 1 and 5, inclusive. As shown in block  326 , the processor calculates for the cart of interest an overall confidence level “% C”, in particular by multiplying each of the percentages %1, %2, %3, %4, %5 and %6 by a respective weighting value W 1 , W 2 , W 3 , W 4 , W 5  or W 6 , by then summing the products of these multiplications, and by then dividing the sum of the products by the sum of the weighting values. 
         [0065]    The processor then proceeds to block  327 , where it compares the calculated overall confidence level % C to the default threshold  186  ( FIG. 3 ). As discussed earlier, the default threshold  186  is a percentage specified by store management, such as 65%. If the calculated confidence level % C is greater than the default threshold, then the processor proceeds from block  327  to block  238 , where the cart of interest is sent for an audit, and then checkout is performed using the product list from the audit. In other words, in  FIG. 1 , the display  69  is used to direct the shopper in the interrogation zone  68  to proceed down the corridor  14  to the checkout area  18 . In contrast, if it is determined in block  327  that the overall confidence level % C does not exceed the default threshold, then the processor proceeds from block  327  to block  239 , where the cart of interest is sent to have checkout completed using the RFID product list  178  ( FIG. 3 ). More specifically, with reference to  FIG. 1 , the display  69  is used to direct the shopper in the interrogation zone  68  to proceed down the corridor  13  to the checkout area  17 . From either of blocks  328  and  329 , the processor proceeds to block  332 , for an exit from the routine of  FIG. 8 . 
         [0066]    The embodiment that is shown in the drawings and described above is configured with a single interrogation zone  68 , through which all shoppers must pass on their way to any of the checkout stations  31 - 36 . Further, the checkout stations are organized into two groups, where checkout stations  31 - 33  in checkout area  17  are used for RFID checkout, and checkout stations  34 - 36  in checkout area  18  are used to audit carts. Alternatively, however, the central interrogation zone  68  could be eliminated, and a single group of checkout stations could be provided, where the checkout stations are all identical. A shopper could freely go to any of the checkout stations. Each checkout station would have its own dedicated interrogation zone. Each checkout station would be capable of checking out a shopper based on either the RFID product list or a cart audit, depending on the result of the interrogation performed in that checkout station&#39;s dedicated interrogation zone. 
         [0067]    The embodiment shown in the drawings is capable of accommodating the presence in a shopping cart  66  of a child  133 , or personal effects. Alternatively, however, in order to simplify the processing task carried out by the image processing software  167 , it would be possible to require each shopper to remove any child and/or personal effects from a shopping cart before the cart enters the interrogation zone  68 . Still another alternative would be to provide shopping carts that lack a child seat, in order to significantly reduce the likelihood that a child may be sitting in the cart when the cart reaches the interrogation zone. 
         [0068]    For simplicity in disclosing the embodiment that is shown in the drawings, it has been assumed that all shopping carts in the store are identical, and thus have the same tare weight. However, some stores have two or more different types of shopping carts, such as traditional shopping carts and flatbed carts. Where there are two or more different types of carts, each type of cart will typically have a respective different tare weight. In that type of situation, each shopping cart would have an RFID tag mounted thereon. As a cart is passing through the interrogation zone  68  and the tags on products in the cart are being interrogated using RFID technology, the tag on that shopping cart would also be interrogated. Based on the information obtained from the cart&#39;s tag, the central computer system  152  would know the particular type of cart that is currently in the interrogation zone  68 , and thus the appropriate tare weight to use in carrying out calculations relating to the weight of that cart. 
         [0069]    Although a selected embodiment has been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.