Decimal

Decimal is an exotemperament in both the dicot and semaphore families of temperaments. It is also the prototypical fully hemipyth temperament, with approximations of √2 at 7/5, √3 at 7/4, √(3/2) at 5/4 and √(4/3) at 8/7, and pergen (P8/2, P4/2), splitting all Pythagorean intervals.

More precisely, it is the 7-limit temperament that tempers out both 25/24, the classic chromatic semitone, and 49/48, the septimal diesis. These two intervals have a rather similar function separating close intervals and creating "major" and "minor" triads (either pental ones splitting the perfect fifth or septimal ones splitting the perfect fourth), and tempering them out allows 5/4~6/5 to be a neutral third approximating √(3/2) and 7/6~8/7 to be a neutral semifourth approximating √(4/3). These can be equated (far more accurately) to 11/9 and 15/13 respectively, tempering out 243/242 and 676/675 and extending this temperament to the 13-limit. Since (25/24)/(49/48)=50/49, it also tempers that out, splitting the octave in two equal parts. As both the generator and period are half that of the diatonic scale, this means it forms mos scales of 4, 6, 10, 14, 24, 38 ...

For technical data, see Dicot family#Decimal

As with many exotemperaments, it is not itself particularly useful, but it has structural value.

Interval chain

In the following table, odd harmonics and subharmonics 1–7 are labeled in bold.

#	Period 0	Period 1
	Approx. Ratios	Approx. Ratios
-2	3/2	21/20, 15/14
-1	12/7, 7/4	6/5, 5/4
0	1/1	7/5, 10/7
1	8/7, 7/6	8/5, 5/3
2	4/3	28/15, 40/21

One can see that the 10-note mos of the decimal temperament contains the 7-odd-limit tonality diamond.