It's not a very clear data sheet []

I think that the retard with very little RPM (long period between pulses) is probably 0 degrees to enable setting the full advance timing. I imagine that as soon as two pulses are seen together in quick succession (i.e. engine has started) that it then retards fully. As the engine speeds up, then the retard is reduced.

10~35 is 25 degrees. If I set it around 28, then I get 3 degrees at low RPM and 28 at full RPM. Sounds reasonable [8D]

Note that the very low compression industrial engines (like SPE) need at least 35 degrees advance to get full power. I think that is why advance is stated as 10 to 35 degrees.