Tiller is the measurement everybody learned once, filed away as a trad-bow thing, and never checked again. I get it. It sounds like something you worry about with a recurve and a flemish string. But your compound has a tiller too, and when it drifts, your bow quietly stops being the bow you tuned.
Thirty seconds. A tape measure. That's the whole check. And almost nobody does it.
What tiller is on a compound
Measure from where each limb meets the riser pocket, straight out perpendicular to the string. Top limb, then bottom limb. The difference between those two numbers is your tiller. Most modern compounds leave the factory dead even or within 1/16".
That number is a fingerprint of your limb bolt settings. If it changes, something moved. And on a compound, the thing that moves is usually you — backing bolts out to drop poundage, cranking them down before a draw-weight check at a 3D shoot, swapping limbs, or just vibration walking a bolt out a quarter turn over a season of shooting.
Uneven limb bolts don't just change draw weight. They change how the cams load, which changes nock travel, which changes where your arrow goes. You tuned a bow with one set of limb forces. Now you're shooting a different one.
The buddy with the high tear
A friend of mine dropped his V3X from 70 to 64 before shoulder surgery season. Backed the top bolt out two turns. Bottom bolt — he lost count. Two and a half, maybe more. Didn't measure anything, didn't think about it, because who measures tiller on a Mathews?
His paper tear went high and stayed high. He chased it with the rest for a month. Moved the nock point. Re-served his D-loop. Almost bought a new rest because the internet told him his launcher arm was weak. Bow shot fine at 20, fell apart at 50.
The fix took one tape measure and four minutes. His tiller was off almost 3/16". We evened the bolts, reset the rest to where it started, and the tear cleaned up that night. A month of frustration against a 30-second check he didn't know to do.
How to actually check it
Hang the bow or have a buddy hold it. Tape measure from the limb pocket junction — where the limb leaves the riser — out to the string, square to the string, not angled. Write down both numbers. Do it when your bow is freshly tuned and shooting how you want, because that's the real value of this check: a baseline.
From then on, it's part of the pre-season once-over. String stretch check, timing marks, tiller. If the numbers match your baseline, move on with your life. If they don't, you just found a problem before it cost you a month — or an animal.
And every time you touch a limb bolt, for any reason: equal turns, top and bottom, and verify with the tape after. Counting turns is how my buddy got here. The tape doesn't lose count.
When tiller actually matters (and when it doesn't)
I'll be straight about the limits. On a well-built modern compound with the bolts bottomed out, tiller almost never drifts on its own. If you max your bow and leave it alone, this check will bore you. Good. Boring checks are the ones that save you when something does move.
Where it bites people: anyone shooting backed-out limbs. That's a huge group — kids pulling reduced weight, anyone coming back from an injury, guys who drop 6 pounds for indoor season and crank back up in August. Every one of those adjustments is a chance for the bolts to end up uneven. The more turns out you run, the more a half-turn difference matters as a percentage of limb preload.
It also bites bow buyers. Used bow off Facebook Marketplace? Check tiller before you tune a single thing. You have no idea what the last guy did to those bolts, and a bow that won't hold a tune sometimes turns out to be a bow that was never even side to side in the first place.
Cam timing gets all the attention — and it should, it matters more. But timing and tiller are the same disease wearing different jackets: both are the bow loading unevenly, both show up as tears and vertical stringing you'll blame on your rest, and both get missed because everyone's staring at the arrow instead of the bow.
Check the bow first. Then worry about the arrow. And when you do get to the arrow, build it in The Forge — get the spine and FOC right so the only variables left on the bench are the ones the tape measure catches.