A short story about usability

I've recently moved house, and last weekend I went for my second grocery shop at Safeway, my new local supermarket. This Safeway has recently installed a new set of 'self checkouts' which allow you to scan, bag, and pay for your own shopping, without a checkout operator involved.

This was the second time I'd used the system, and the first time had passed without incident — it was even a little bit novel, a tiny bit fun to scan my own items and bag them myself. But the second time was different.

This time, I had more than one bagful of items. As I finished filling the first bag, I went to take it off the scales — the bags are weighed to make sure you don't slip anything extra in — and the POS system beeped at me. "Please replace item such-and-such," it asked me.

So I put the bag back down. "Please replace the item," it asked me again, tonelessly. So I removed the bag and put just the item in question (a packet of biscuits) back onto the scales. But no luck, the system simply refused to allow me to proceed. It wouldn't recognise that I'd put the biscuits and/or bag back onto the scales, no matter what I did.

Growing increasingly frustrated, and with a growing line of people waiting too (installing self checkouts allows Safeway to cut down on the number of express checkouts open) I signalled to one of the brightly-vested 'experts' hovering nearby. I explained the situation, and he whipped out a PDA and tapped out a command to allow the POS system to continue.

"Out of curiosity," I asked him, "what did I do wrong? Just so I know for next time."

His voice was curt as he replied, "You can't remove a bag until the big dollar sign is flashing."

Obviously.

My experience with the system illustrates perfectly how not to design with usability in mind. Members of the public will be using the self checkouts without any training, and even as I used one I could see other people getting frustrated with their experience as well. If you are dealing with an untrained userbase, things should be as obvious as possible. There should be very little room for mis-interpretation.

Adding a flashing dollar sign (next to a button marked 'finish and pay', not what I wanted to do) is far from a simple and obvious way to tell users, "it's okay to start packing a new bag now".

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