Create a helix spiral. Assign its parameters to an external design table. You can format that excel table like the picture you posted
External design table is no less global than "global variables". My question was about finding a local way to provide driving values.
Search this forum for involutes, gears, gear tooth, etc.
This has come up many times and there's probably some wisdom in here already that can be of use to you.
Click the magnifying glass icon in the upper right of this page.
I have done exactly that (and always try to search for existing answers before filing a new one).
The issue is not about the tooth, but about providing design parameters locally, within a sketch.
Maybe that's simply not possible (except for measures, with the Smart Dimensions tool).
I think my question was a bit premature.
The "Equations" part of Equations manager has the formulas used in a sketch. Within the sketch (when you carefully exit Smart Dimension, and then click on a dimension), you get "Edit Equation...". It's worth noting the sigmas in front of your dimensions, telling they are derived from an equation.
Within the equations editor, I can also make equations within the sketch derive from each other (I think... yes, I can ).
Furthermore, I think my original thinking of even needing "local variables" was misguided. If I need a tooth, it needs to fit another tooth. Thus, these design inputs really come from a larger context than that of a sketch.
From my side, problem solved. Keeping the entry here in the hope that it helps someone find the way the tools' intended to be used.