Hi Barry,
Some math would seem to be in order.
The screw turns with constant RPM, but the horizontal velocity of the bottle in mm/cm/meters per second, varies between constant sections, and variable section.
The horizontal velocity in the variable section also is not constant. (?)
The constant sections have constant horizontal velocity.
There are formulas to convert Pitch to Lead.

So the horizontal range must be split up into different velocities with some Logic.
Say the fastest constant section uses the straight clock.
When in a slower constant section, the bottle speed, or clock, will have to be adjusted down.
When the bottle is in the variable section, Multiply or divide the variable sections clock by the conversion equation(s).

The original litegraph had a bunch of functions...

- Brian