ReadonlynameReadonlyplacePaper position of each sample, in mm from the beginning of the roll.
ReadonlysecondsReadonlytravelPosition on the printed ordinate of the roll's own ruled band: 0 at that half's P.P. gridline, 1 at the shared F.F. line, with M.F. at 0.5. For a pedal, 0 with it up and 1 with it down.
Both Welte scales rule that band the same way — five rails, "P.P. M.F.
F.F. M.F. P.P.", three named levels a side with the centre F.F. shared,
measuring 20.0 mm between rails on red 3309 and on green Welte 184 alike —
so a curve from one system and a curve from the other are in one unit, on
Welte's authority rather than on ours. That is what lets a red issue and a
green issue of one recording be compared at all. It is a unit of drawn
deflection: whether the deflection is linear in the bellows' own travel is
open, and is what the emulator's scaleWarp exists to answer.
A curve sampled along the roll: where each sample lies on the paper, when it passes the tracker bar, and how far the bellows or the pedal has travelled there.