Left Turn Phase calcs from MODOT EPG

I'm trying to understand the calculations for capacity criteria for Permissive-Only and Protective/Permissive Left turns that are given in the Missouri Dept of Transportation EPG. In section [902.5.23 Signal Indications for Left-Turn Movements – General (MUTCD Section 4D.17)] where the Permissive Only and Protective/Permissive left turn calcs are under "Capacity Criteria" it shows VLT+VO<600x(gp/cp) and (VLT)pp+VO,1200x(gpp/cpp). Where do the numbers 600 and 1200 come from? What are these numbers representing?

I work in a smaller city and am wondering if I can scale these calculations to better fit the capacities I'm studying. So knowing what these numbers are for will help me determine if I can scale.

Thanks!