This is a post by Evan Winter in his presentation.

Discusses how you can input a known mass value for a part of assembly instead of calculating from geometry and density material.

Check out slide 23 of his presentation here.

Suggested reading – http://support.ptc.com/help/creo/creo_sim/usascii/index.html#page/sim/simulate/modstr/idealizations/reference/guide_assgn_massprops.html

Content Source: Evan Winter/PTC