Ischial Variation is the measurement of the distance between your sit bones.
How to measure it:
If you don’t have the possibility to go to a biomechanics expert or to a shop that has a sit bones measurement tool, you can easily simulate the procedure at home using corrugated cardboard or another moldable material on a flat surface.
Sit at 90° and apply pressure.
Find the centres of the two ischial impressions and measure the distance between these two points with a ruler. The result is your ischial distance.