How did Solidworks determine the variable pitch of the helix?

Dear Everybody,

With the constant pitch I know that, Height=Pitch x Revolution.

But with the variable pitch I don't know the way how did Solidworks determine the variable pitch?

In the Region parameters table when I input H and Rev, P(variable pitch) is determined automatically by solidworks.

Could you please to help me the way How did Solidworks determined P(variable pitch)?

Thank you very much.

SolidworksGeneral