I had a housemate who was the personification of exasperation when it came to those self service check outs.
I insisted that he help me with the shopping as half of it would be his.
Every time and without fail, he would do something to set off the automated voice of the scanner. He would especially remove the bags from the metal pan causing the voice to say "Please return the item to the bag" he couldn't get that right and so the voice would say, "There is a problem with this item, please wait for a member of staff" so we'd then have to wait for an over worked scanning supervisor to give us their attention which of course would mean I would get a lecture about not doing what numb-nuts had just done.
The most infuriating thing about this was that in the presence of the scanning supervisor, he would say "See!" in a sanctimonious tone that implied it was MY fault!
I think that was his way of trying to get out of the shopping. It didn't work!
I think, as someone else has explained already, that the pans you put your shopping on weigh the goods in the bag which correspond to part of the bar code which tells the computer the weight of that item. It's a pretty simple process of Net Weight (The weight of the load), Terr Weight the combined weight of the load and container and Gross Weight the weight of everything combined.
In 2011 a British Celebrity Chef, Anthony Worral-Thompson stole items from Tescos by not passing them over the scanner. It seems the security staff were on to him, had observed him but knowing he was a celebrity and someone who had the ability to harm the reputation of Tesco, they kept him under observation and again observed him selecting an item which he then concealed and left the premises via the point of payment, making no attempt to pay.
http://www.dailymail.co.uk/news/article-...Tesco.html
Naughty, naughty boy!