TLDR; Tesco self service tills let you buy your groceries without waiting on a person, but when they don't have any coins left, confusing UI reigns supreme - all for the want of a comma.
This isn't a biggie, but I thought it was interesting.
Tesco is a chain of shops that sells pretty much everything, although its bread and butter business is selling - err - bread and butter, and whatever other food stuffs you can think of. It's actually Britain's leading retailer with £1 in every £8 spent in the UK spent in a Tesco and as a result of this its shops can be pretty busy places at peak times. Think of it as the UK equivalent to Walmart.
To speed up the checkout process Tesco uses automated checkout machines where customers scan their own goods and bag their items themselves. This is great for the most part; customers can pay with card or with cash and they can even get the right change for their money. Automated tills take up half the space a human-operated till does so you can process more people at once and - best of all for Tesco - automated checkouts don't expect a wage bill at the end of each month.
But they're not perfect.
But they're not perfect. Just like vending machines and ATM's, Tesco's automated checkouts can run out of money to dispense to the customer. When that happens; when it can't give you the right change; what does it do? Well, it switches to a "Cards Only" kind of survival mode where it can still process your order so long as you're paying by card.
Pretty handy right? But can anyone spot the UI mistake in the second picture? The "Start" button changes to read "Start Cards Only". There's ambiguity there. What the heck is a "Start Card"? I have actually heard people ask that question to one another in the queue. In-fact, I've actually been able to skip the queue because people reckon they can't use the automated checkout because they don't own a "Start Card".
Queues actually form and put stress on the manned checkouts, all because people think they need something called a "Start Card", and all because some UI designer somewhere neglected to enter a comma.
"Start, Cards Only"
UI is important and this is a small example of how slip ups in interface can have real-world consequences.