I was convinced that it was because at the time h2g2 was written, "digital watches" were actually LED watches, which required that the user press a button to se

I was convinced that it was because at the time h2g2 was written, "digital watches" were actually LED watches, which required that the user press a button to see the time displayed for a few seconds! (also the case for some of the first LCD models) low power LCD watches were popularised in the early 80s