h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

While it's a useful summary of the time and date there is an error in the article and one other bit which could be a little misleading.

When talking about digital watches and millenia it says that watches are often set to work from 1901 to 2099 because 'rule one applies', which is the rule about years divisible by 4. While this is true for the year 2000 it isn't true of most millenium years. The year 2000 was a leap year because it was divisible by 400. It won't, for example, be true of the next millenium year. 3000 won't be a leap year and neither was 1000.

Possibly misleading is the statement that clocks are retarded at 2am in the UK. While this is true I felt it was said in such a way that I initially read it as meaning that both the clock changes in the year happen at 2am. They don't. The occur at 0100 GMT, which in October is 2am but in March is 1am.

Sorry for the delay, but I'll get back to this in mid-July. See my journal if you want the gory details.

Sorry for the delay in returning to this.

You are of course correct, in that rule 1 only is correct only for the even millenia. It is also the case that rule 1 only is correct for every digital watch ever made, and any one likely to be made in any time frame which I will be aware of.

In an early version of this entry, I did describe in detail the logic needed to decide if a year was a leap year, using BCD digits, but this was deleted in peer review. The point that using rule 1 with rule 2 goes wrong in the year 2000, whereas rule 1 alone survives year 2000 without error, could perhaps be better expressed now.