Does anyone know the official specs on where to measure the idle & cruise portions of the meetering rod diameter?

I can certainly sample what I have and come up with a number, but I'm curious if there is an "official" specification somewhere out there???

Oh, asking because I have a 2357 rod here, currently using 2004, trying 2159 (which is a tad leaner than 2004), but judging by the looks of it the 2357 is even leaner, and I think I need to go down that route. Power is easy to measure, idle...ummm, you can sort of guess-timate it, but cruise...man, somewhere on that path the transfer starts, but it's hard to tell where.

Thanks!

EDIT
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So when I'm thinking of a spec it would be from the short "L" shaped part where the rod hangs from the meetering tree, basically the distance from that 90 deg turn to where on the body of the rod to measure the diameter. I have seen many rods where the rod length varied, therefore, I do not think you can go the easier route and measure from the opposite end?