Dropping summer time

It seems moves are afoot to stop the clock changes, and I rather like the idea.

The issue, for me, is that people talk of "permanent summer time" as the answer, sort of forgetting that the clocks are set based on lots of measurement at the Greenwich observatory and hence why we have Greenwich Mean Time. It is summer time that is the "anomaly" and it only makes sense to me to be on GMT all year.

This assumes stopping clock changes is a good idea, and that seems to be a matter of debate, but one which is leaning towards the idea of not doing it.

So, some thoughts on why, to my mind, it is obvious we stick to GMT all year.

The matter of definition

It is called GMT, and is generally the high sun at the middle of the day at 12:00. It would be crazy, IMHO, to have the mean time over Greenwich as Greenwich Mean Time plus one hour.

What would we call it?

We can't call it GMT and it makes no sense to call it BST as not only summer time. It won't be UTC if +1, so actually we need a new name. That is more of a pain that you realise as it is a lot of software and all sorts. UKT maybe?

It only matters in winter anyway!

In summer we have more than enough daylight. Yes, moving some "unused" daylight from early morning to evening is vaguely helpful, or was before the invention of street lights. But what matters is Winter.

We tried a permanent summer time in 1970 and it did not go well. We know GMT in Winter "works" well enough and fits around schools and so on.

Changing what we do in Winter (by making permanent UTC+1) would be way more problematic as we simply have less daylight to play with. Changing in summer (by stopping BST) is not an issue as we have daylight to spare, so to speak.

Give UK an advantage?

There are a lot of things that log in UTC, and confusion over UTC and local time happen all the time. Heck, even the Amazon app gets the order date wrong all summer because of this. BT get this wrong in their XML in lots of places. There is an advantage for the a country that stays on UTC+0 as their time zone as all UTC logs will be local time, and simpler for everyone.

Some have even suggested that UTC should be moved to the middle of the Atlantic so no country is UTC+0 and hence has any advantage. Let's give the UK that advantage.

Countdown and clock changes

As I mentioned, for the Brexit clock, I had to allow for the clocks changing (something many such countdown clocks do not allow).

Basically, one of the days between now and (the current) Brexit is 25 hours long. This, in itself, is not complex.

I have tinkered with the way I do this a few times, and eventually came up with this, starting with how many whole days...

• Work out a time for UTC midnight on target date
• Work out a time for UTC midnight today
• Divide time difference (as seconds) by 86400 (a day) for number of days
• If the current local time (HH:MM:SS) is on or after the target local time (HH:MM:SS) take off one day from that total.

That is the easy bit, and means that the number of days changes at the local time (HH:MM:SS) of the target, so for Brexit, changes at 11pm local time exactly each day. What normally happens is the time part then counts down from 23:59:59 until 00:00:00 at 11pm local time the next day.

However, working out the time part is one area that took me a bit of thought. In the end I make use of the fact that linux mktime() function allows tm_mday to be any value and it adjusts.

So, what I do is :-

• Create a date for the target date/time, local time.
• Subtract the calculated number of days from the tm_mday part of that.
• Work out time difference from that point to current time, and convert to hours, minutes and seconds.

The effect of that is that once the day changes, the time part goes down without a discontinuity. It means that on the day that has the clock change the clock will start counting down from 24:59:59 instead of 23:59:59.

For Brexit, that means that 11pm on Saturday 26th October 2019 it will go to from 5 days 00:00:00 to 4 days 24:59:59 and count down for 25 hours until 11pm on Sunday 27th October when it goes to 3 days 23:59:59.

Of all the ways to work this out, I think this is the best. It means days are counted to the local time on each day that matches the final target local time (so for Brexit, its counts a day at 11pm local time each day), and then that the time part counts without a discontinuity down to 00:00:00 at the same local time the next day.

Yes, I put far too much thought in to this.