TCL: how to count the nodes selected?

Dear members,

I tried to applied force on nodes. The total force is a constant. But the mesh changes every time, so I want get the force applied to every nodes by calculating (total force)/(total number if nodes selected).

Does anyone know how to get the total number of selected nodes by TCL?

I tried hm_count, but I can not find a example of hm_count. As well, I don't know which variable is used to save the number in hm_count. Or hm_count return a value?

Thanks a lot!

Richard