There are two parts to your question, if I understand it correctly

1. You can always use the the standard DMV's to see the formula and the MDX used to define any calculated members. One such is $system.mdschema_measures. Also, you can open the calculations tab and view the MDX for the measures.

2. For gross shipped dollars, this is a fully additive measure and you should be using a SUM() function on the column to calculate the measure