The formulas only produced approximations, and then rounded to 5-second boundaries because the tz data format didn't have enough bits.
Little known fact: if you have a sub-minute-resolution UTC offset when a leap second hits, it rips open a hole in the space-time continuum and you find yourself in New Netherlands.
________________________________________ From: Tim Peters email@example.com Sent: Saturday, July 25, 2015 00:07 To: ISAAC J SCHWABACHER Cc: Alexander Belopolsky; Lennart Regebro; Python-Dev Subject: Re: [Python-Dev] Status on PEP-431 Timezones
Sure. But, honestly, who cares? Riyadh Solar Time was so off-the-wall that even the Saudis gave up on it 25 years ago (after a miserable 3-year experiment with it). "Practicality beats purity".
Heh. It's even sillier than that - the Saudis never used "Riyadh Solar Time", and it's been removed from release 2015e of the tz database:
https://www.ietf.org/timezones/data/NEWS Release 2015e - 2015-06-13 10:56:02 -0700 ... The files solar87, solar88, and solar89 are no longer distributed. They were a negative experiment - that is, a demonstration that tz data can represent solar time only with some difficulty and error. Their presence in the distribution caused confusion, as Riyadh civil time was generally not solar time in those years.
Looking back, Paul Eggert explained more in 2013, but it took this long for the patch to land:
http://comments.gmane.org/gmane.comp.time.tz/7717 > did Saudi Arabia really use this as clock time?
Not as far as I know, for civil time. There was some use for religious purposes but it didn't use the approximation in those files.
These files probably cause more confusion than they're worth, so I'll propose a couple of patches to remove them, in two followup emails. I haven't pushed these patches to the experimental github version.
The position of the sun is vital to establishing prayer times in Islam, but that's got little to do with civil time in Islamic countries. And Olson didn't take his "Riyadh Solar Time" rules from the Saudis, he made up the times himself: "Times were computed using formulas in the U.S. Naval Observatory's Almanac for Computers 1987". The formulas only produced approximations, and then rounded to 5-second boundaries because the tz data format didn't have enough bits.
So, as a motivating example, it's hard to get less compelling: Riyadh Solar is a wholly artificial "time zone" made up by a time zone wonk to demonstrate some limitations of the tz database he maintained. Although I expect he could have done so just as effectively by writing a brief note about it ;-)