Errrr, I've been in heated debates over that.
IMHO -
Not at all,, or at least not neccesarily anyways.
I consider the
measure a relatively rough estimate at best. Maybe in perfect world it would. But not in my world.
Tons of variables to be considered. Things like efficiency of the design, head weight, are shafts tapered, string weight (if silencers, clickers, etc. are used), nock fit, amount of center shot if any, and there's probably more.
I use it for comparative evaluations mostly.
I'll find a arrow that shoots good, measure the spine, try a couple above and below. Then I try and find additional arrows in the middle of what seems to work.
Also, way too many times I'll order 60# shafts (0.433 deflection I think). I'll check them when I get them and if they measure .650 to .520 (40 to 50#) I'll call and get them exchanged or refunded.
Without a tester you'd have no clue until you've made them and then it's too late.
Never had a supplier argue with me if I threw numbers at them.
If I'm paying for steak, I don't accept pot roast.