The 640 equal divisions divides the octave into 640 equal parts of precisely 1.875 cents each. It is contorted in the 5-limit, tempering out the vishnuzma, |23 6 -14>, with the same tuning as 320edo. In the 7-limit it tempers out 19683/19600 and | 16 2 -1 -6 > and in the 11-limit it tempers out 540/539, 8019/8000 and | 14 -1 -2 -4 1 >. It provides the optimal patent val for the rank three albus temperament tempering out 540/539 and 8019/8000, and the 125&130 temperament.

← 639edo 640edo 641edo →
Prime factorization 27 × 5
Step size 1.875 ¢ 
Fifth 374\640 (701.25 ¢) (→ 187\320)
Semitones (A1:m2) 58:50 (108.8 ¢ : 93.75 ¢)
Dual sharp fifth 375\640 (703.125 ¢) (→ 75\128)
Dual flat fifth 374\640 (701.25 ¢) (→ 187\320)
Dual major 2nd 109\640 (204.375 ¢)
Consistency limit 5
Distinct consistency limit 5