Fractional sharp notation

The letter notation is a notation scheme developed by CompactStar for just intonation up to the 31-limit and some regular temperaments. It is Pythagorean notation with the letters H-Y used as accidentals for higher prime limits (starting from H to avoid conflict with note names). These are fairly easy to memorize as they go in alphabetical order as the prime limit increases.

Accidentals

Prime limit	Letter	Ratio	Letter	Ratio
5	H	81/80	I	80/81
7	J	64/63	K	63/64
11	L	33/32	M	32/33
13	N	1053/1024	O	1024/1053
17	P	4131/4096	Q	4096/4131
19	R	513/512	S	512/513
23	T	736/729	U	729/736
29	V	261/256	W	256/261
31	X	32/31	Y	31/32

For example, 5/4 is IM3 and 7/4 is Km7 (spoken names, if mechanical-sounding, can also be made out of these like "I-major third").

This system can also be used to notate regular temperaments (including both equal temperaments and rank-2 or higher). For example, 24edo could be notated by using 12edo notation together with L/M to denote the tempered 33/32 quartertone of 50 cents:

Notation