The Lorythmic scale is empyrical and defined so that a 1 SW-point difference is what Bobby Jones still could distinguish.
Where MOI measures the resistance around the wrist (and could be called Release Weight), SW measures the resistance around the elbow (hence Swing Weight).
Adams who invented the SW-scale stumbled (by accident or not) upon that measuring on a fulcrum (using standard grips) is basicly a smart shortcut to measuring MOI.
Measuring on a 18.2" fulcrum or
Release Weight = Total Weight gr x (Balance point" - 18.2")
would give you a pretty good approximation of constant MOI.
And RW = Release Weight / 35 - 81 and replace the 1st digit with the coresponding letter in the alfabeth would give you similar values and "Bobby Jones precision" as the Lorythmic scale for SW.
I put this to the test with a P,7 and 4 iron I build using a pendulum and tachometer to have them constant MOI :
Club Balance Weight RW RW SW
P 27.21 460 4148 C7.5 D0.6
7 27.66 438 4145 C7.4 C8.7
4 28.11 418 4144 C7.4 C7.0
