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If you were to build a clock and had to choose between indicating AM or PM, such as with a single LED indicator, which would you choose and why?
I have seen commercial clocks using both approaches, with the LED being lit for AM and PM, with PM being more prevalent, but is one better than the other?
If you were to build a clock and had to choose between indicating AM or PM, such as with a single LED indicator, which would you choose and why?
Which is the ambiguous condition? If the clock reads, say, 9:00 - which situation is ambiguous?
Evening is when it's ambiguous. Is the clock military clock? Since you only have one light, have your LED light for indicating evening.
The reason PM is better is because it helps clarify the more ambiguous situation.
Consider an interface like this:
It can just read nicely.
The approach in question is not a good approach since it includes an element of cognitive friction that will make things really hard for an user. If there's a technical reason to use just one LED, then it would be better to look for a different approach. Either AM or PM should be lit at any time as it fits.
There really isn't much more to say to this, UX is not for "guessing", it's meant to make user's experience better.
An alternative path, assuming this is a digital clock, would be to use a 24 hours clock (also know as military time), but this approach would be useful only in countries where this way of measuring time is commonly accepted.
Analog clock faces don't have an A/PM indicator because they're never mistaken for 24h clocks. In digital clocks, I'd try lighting only the lower dot of the colon for 12h clocks, because "1.23 pm" is much better established than "13.23". You could then also test only upper dot = PM.
