Back in the dim and distant early days of bar coding for pricing I remember not being able to by something from Asda at Charlton because the checkout didn't recognise the bar code. Even though the goods carried a sticker with the price on, no one, the checkout operator or the floor manager or the store manager were prepared to let me pay the sum concerned without their being able to log it on the system as sold.

Of course these days bar codes are everywhere and they are completely reliable. Well, maybe yes maybe no.

We are all used to watching our goods being slid across a laser scanner at the till or using a hand held scanner to check our goods as we go. Then we are presented with a bill which we normally accept without query.

I'd suggest that we start to take more attention.

I have had several problems with Sainsbury's hand scanning system where on more than one occasion on their spot-check rescan I was found to have somehow scanned 1 item twice. I could understand this if they followed each other consecutively on the bill but they hadn't.

A glitch - yes of course - but a glitch which would have cost me money. OK not a lot but a goodly number of 'not a lots' eventually adds up to a fair old sum.

Today however I was scanned (well my shopping. not me) to the point of incredulity by something happening which I had never considered possible before this happened.

I had been out to purchase a 500Gb external hard drive for the 'expanding like topsy' network at Naq Towers.

It was £39.99 plus vat.

I got to the check out with the drive and a few other bits and bobs which were all scanned and my bill calculated.

Here I admit complicity with the problem as i was on the phone. I vaguely heard the sum quoted at me; I put my card in the reader and entered my pin; I took my receipt and it was at this moment that my brain started to smell a metaphorical rat.

How much did she say?

I looked at my receipt and it was for £185.88 massively higher than it should have been.

The reason being that, apparently I had bought a Candy dishwasher for £149 plus vat. As for the hard drive - I had bought it not!

I showed this to the checkout woman who immediately called the line manager.

Having showed her that I clearly had no dishwasher about my person we began the trial of working out how the hell the system had decided that I did have.

They scanned the bar code and it came up as a hard drive. However there were 4 bar codes on the box, all different.

So I suggested they checked them all since they were only a matter of a few millimetres apart. When they scanned them, two were unrecognised but the third, directly beneath the required bar code scanned and was accepted as the dish washer.

I was under the impression that this was as near as damn it impossible.

Now you imagine if the item was only a few pounds different and, like in many stores, the item name is a meaningless collection of abbreviated words.

Would you have realised that you'd been ripped off by a machine error?

I suspect not. Similarly I suspect that this is perhaps more common than we know.

In my case the difference was a £129.25 refund in my favour however I am forced to wonder just how many times my bills haven't been what they should be; be that to my or the stores benefit.

We have all this technology to speed us through the tedium of purchasing but is it really as reliable as it should be? And further more would we ever know ?