The notes of the copy that found their counterpart on the other.
How far the counterparts still lie apart, as a root mean square in the other copy's millimetres.
The standard error of the scale, as for a line of least squares through the matches: the residual over the spread of the matched notes along the copy, and over the root of their number. The robust line is fitted otherwise, but on Welte 225 this comes within a few per cent of what resampling the matches gives.
Applied before the scale.
How a copy's places are carried onto another copy's:
x_other = (x + shift) · scale.