Points is from the Typography world, where there are 36 points in 1 inch.
Units is from the CAD world and is the units is the default for the drawing (in, mm, etc.).
So if you picked a size of 18 points, the Units will change to 0.5 inches (about 12.5 mm).
Or if you picked 1 inch (25.4 mm), the points will change to 36.
My proportion is 25.4/96=0.26458 , means 96 point in 25.4 mm .
Tanks very much.