International Standard. If you look across the corporate world you will always see an R vs TH on calendars using single character abbreviations.
-- Six Demon Bag Jack Burton: Hey, what more can a guy ask for? Egg Shen: Oh, a six-demon bag! Jack Burton: Terrific, a six-demon bag. Sensational. What's in it, Egg? Egg Shen: Wind, fire, all that kind of thing!
i've never heard of that. And I've been coding calendar tools for websites and databases for years now.
I didn't do it to meet any international standard, but I thought it was a pretty useful convention to remove ambiguity when I was at university (which used R instead of T in it's scheduling).
I looked for a good while off google and wiki and couldn't even find an indicator of anything having to do with using R for Thursday. I'm intrigued to say the least regardless of the countless people telling me to fix a fubar.
My experience was at school, like I said. They used R for the calendar in the scheduling to remove ambiguity when presenting the schedule something like this:
Class 101, MTF, 10:30-11:20
Which, unambiguously means Monday,tuesday,Friday
Compared with Class 102 MRF 10:30-11:20
Which unambigously means Monday,Thursday,Friday
It was that that I found so intriguing and why I decided to use R for the calendar.