In message , at 08:30:30 on Tue, 18 Sep
2012, Roland Perry remarked:
The first question Tesco ask you is "Have you brought your own bag",

It's on the same initial screen as "Press to start scanning" (or
whatever the exact words are).

at which point you can put it on the bagging area and it
re-calibrates the weighing scales.

The machines at my local Sainsbury's don't seem to get on with rucksacks
whenever I've tried that. They can cope with normal cloth shopping bags
of the sort I seem to acquire at conferences.

Perhaps because a rucksack might not properly distribute the weight
when placed on the sensor, whereas it's easier with a cloth shopping
bag?

It's possible it's an anti-theft measure, to make sure you don't put
your own bag on the scales with some [un-paid for] items *already* in
it. I might try that next time I'm in Tesco (go in with my own bag but
also a brick or some other item I could not have bought in the store).

So I took two (empty) hessian "green" bags, and this was too heavy for
the scales, and an assistant was summoned.

I was also overcharged when an "any two for £3" offer wasn't triggered.
After much puffing and blowing (and two visits to the display shelves by
the customer service rep) I eventually got a refund of 2x the
difference. Once upon a time I think they gave you that, plus the
product for free.
--
Roland Perry