173zpi

173 Zeta Peak Index (abbreviated 173zpi) is the equal-step tuning system derived from the 173rd peak of the Riemann Zeta Function.

Theory

173zpi is the strongest zeta peak within ±0.5 divisions of 39edo, and serves as a compressed-octave version thereof (2/1 ≈ 1196.204¢), narrowing the octave by ~3.796¢. 39edo, being a zeta valley EDO, poorly approximates Just intonation relative to its step size. Its harmonics routinely exceed 30% relative error, so using 173zpi instead—the strongest zeta peak within 39edo's vicinity—is a logical way of correcting for this, if desired.