How to get Machining Hight dimension from bottom face

Hi,

I want to show machining height dimensions of faces from bottom face in the plan view of casting.
I need a macro that will do the following.
1. Select reference face (Base of casting)
2. When I select different faces, the distace of selected face from reference face should come as note near mouse click.

Pls help me out.

SolidworksApi macros