To start with a curve, the best way to doit is to make a straight line started with the original ignitionpoint of the engine.
Normaly the advange is not more the + or - 5 degrees of the original ignitionpoint.
Race-engines can make more degrees, sometimes they make + or - 15 degrees of the original ignitionpoint.

A twostroke engine like a weedeather have a ignitionpoint ~30 degrees BTDC.
If you gone make a advagne curve, you have to start with a line 1000rpm till 8000rpm 30 degrees BTDC.
To make this line you only need two points into the tablemaker, one at 1000rpm and one at 8000rpm
If the engine runs smooth with this advange ignitionline, you can change the 8000rpm point to put the point down to 25 degrees BTDC.
If the engine runs better, you can ad more points to the line and change the BTDC-points of the line.

NEVER START WITH MORE THEN 5 DEGREES DIFFERENS BETWEEN THE ORIGINAL IGNITIONPOINT AND THE ADVANGE.