A circular chord progression, which can only be executed when the tuning allows every adjacent pair of chords in the progression to have at least one common-tone.
The most typical example is the one in 12-edo which is normally described in harmonic analysis as I - vi - ii - V - I, in which the syntonic comma is tempered out; hence the name. I give a very full description of the discrepancies between the 12-edo and just intonation versions of this progression in the xenharmonic bridge definition.
A different example of a "comma pump" progression, composed by Graham Breed in blackjack tuning, may be found about 4/5 of the way down on Monzo, The Blackjack Scale.
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