To the nearest half-hour.
As readers of Taming the Turing Machine know, I'm a big fan of the product editing process. I believe some of the best designs come from relentlessly stripping away the functions of a product until just the essence is left. In the digital world, it's so cheap to add extra features that we have to be constantly vigilant, lest they somehow creep into our products without our noticing and crowd out the good stuff. In the physical world though, every feature costs money, so if you want to sell something cheaply, you'd better make it simple. I came across a great example of both at my local DIY shed when I bought a new set of Christmas lights this week.
These days even Christmas lights have software in them, the better to make them flash in a variety of only slightly different but equally annoying ways in addition to the one aesthetically pleasing way (always on). What is the point of that? Every time I turn them on I have to press a button seven times to get to the setting I want. The feature I want is obscured by six features I don't want. They're LED too of course, and energy-efficient as a result, but it still makes sense to turn them off when they're not needed. And what better way to do that than a nice, old-fashioned, mechanical timeswitch?
There they were, hanging right by the Christmas lights. A simple, does-what-it-says, honest-to-goodness analogue mechanical 24-hour timeswitch for just £1.99. When you consider that 33p of that goes to the UK government in tax, and another (perhaps) 75p to the retailer, we're left with a timeswitch that must have cost less than £1 at the factory gate. The only catch? Not, I hope, that's it's going to catch fire and burn my house down the first time I use it. Or that its idea of 24-hour timekeeping isn't the same as mine. Just that you can only program the on/off times in increments of half-an-hour. You know what? I don't care. For turning on and off my Christmas lights (not to say virtually every other application I can think of), half-hourly resolution is just fine. Hell – I'd even have been happy with hourly.
Imagine what would have happened instead if the timeswitch function had been integrated into the Christmas lights. It could so easily have been, with just a little bit of extra software. I'd have had minute-resolution, but "To set the time, press and hold button A until lights flash three times. Then press button B once to advance the hours. Lights flash 13 times…" , and so on. You get the idea. So congratulations to B&Q. I know you were motivated by money (so was I when I bought it), but the effect on usability was great too.