What is the calculation of normalBias?

The doc says that

I want to know how the normalbias calculated?And how to set normalBias to fit the different scene?

The normal bias is user-defined (with a default of 0). It’s usually found experimentally, testing values until you find something that works. It’s good to set a value as small as possible while still avoiding shadow acne, as a value too high can cause other artifacts to appear in the shadows.