Base Commit BP Reverse Auto-Populate Related Change Commit BP Values

Hello,

I've studied the Out of the Box (OOTB) BPs for Contracts and Change Orders. I'm trying to better understand how the subtotal fields are updated between each other. More specifically, on the Contracts BP upper form "Initiate Request", there is a read only field for Net Changes by Change Orders and another read only field for Revised Contract Amount. In my simple mind I'm thinking that these fields are populated by some other method that goes to the related changer orders and sub-totals the data.

I opened the field properties for Revised Contract Amount and saw that it was populated by Formula: Original Contract Amount + Net Changes by Change Orders. That makes perfect sense to me.