My car has, of late, had a problem where one or both of the battery terminals comes a little loose (I could probably tighten it down and be fine, but I haven't yet) so occasionally I'll have to pop the hood and jiggle a wire to get it to start. This resulted in my car stereo theft-lock being activated (I'm sure I posted about that, but can't find it -- ah well) at one point. It resulted in it being activated again today (but I knew the code this time, having set it myself) and so the clock was also reset.
Given that my car begins the move to PDT in ~40 hours I decided to set the stereo clock to PDT. I happened to be in EDT at the time, and was on the road with a destination of EST.
That meant that when I was glancing at my stereo clock to see if I was going to make it on schedule I was having to 1) remember in what timezone the target time was 2) remember to what timezone my clock was set 3) remember how many hours were between them 4) add. Which was only a problem given that I was doing this every 15 minutes or so and wasn't caching previous results for some reason.