Pull up any setup video and you'll hear the same number. 13/16ths of an inch from the riser. Some guys say 7/8ths. Easton has a chart. Everybody's got a starting point and everybody treats it like a finish line.
It's a starting point. That's it. Center shot measured with a ruler gets you in the parking lot. It does not get you to the door.
I've tuned bows that shot bullet holes at 11/16ths and bows that didn't settle until the rest was kicked out past an inch. Same arrow. Same draw weight. Different riser geometry, different cam lean, different rest, different shooter. The number on the chart doesn't know any of that.
What center shot actually is
Your arrow leaves the bow flexing. It bends around the riser, recovers, bends back, recovers again. That's archer's paradox and it's been happening since people shot sticks off the side of a stave. Center shot is your attempt to point the arrow so that when it's done wobbling, it's going where you aimed.
The ruler method says: line the arrow up with the string, the berger hole, the center of the limbs, whatever reference you trust. Get it visually centered. And that gets you close. But "visually centered" assumes your arrow's stiff side, your cam lean, and your grip torque all cancel out to zero. They don't. They never do.
Two bows off the same rack will want their rests in two different spots. One has a cam leaning a hair left from the factory. The other got a string twist during setup that nobody logged. You'll never see it with a ruler. You'll only see it on paper and downrange.
Why the ruler lies
Here's the part that trips people up. A bow can shoot a perfect bullet hole through paper at 6 feet and still not be on center shot. Paper at close range hides a lot. The arrow hasn't had room to do anything yet.
The truth shows up when you back up. Walk-back tuning is the real center shot test, not paper. You shoot a vertical line at 20, then 30, then 40, then 50. If your groups march left as you back up, your rest is too far right. March right, rest's too far left. The paper tear at close range can read clean the whole time while your arrows are quietly drifting two inches per ten yards.
I had a buddy — shoots a Mathews, good shooter, better than me at 20 — who could not figure out why he was dead-on at 30 and four inches left at 60. Paper tuned perfect. He'd measured center shot three times with a caliper. The rest was sitting exactly where Mathews said it should. We moved it in 1/32nd of an inch, a hair most people would call a rounding error, and his 60-yard group walked right back to center. A 32nd. That's how fine this gets.
Broadheads make it even louder. A fixed head is a wind vane bolted to the front of a poorly-aimed arrow. If your center shot is off by a hair, field points forgive it and broadheads won't. That's why guys think their broadheads "don't fly" when really their rest's been a 32nd off the whole season and the field points were just polite about it.
How to actually find it
Forget the number. Start near the chart spec so you're in the neighborhood, then let the arrow tell you the rest. Bareshaft and walk-back are your instruments, not the caliper.
Shoot a bareshaft next to a fletched arrow at 20. Where the bareshaft lands left-right tells you which way to nudge the rest. Bareshaft left of fletched, your arrow's reading stiff, move the rest a touch. Then back up and walk-back tune to confirm it holds through distance. When the bareshaft stacks with the fletched group at 20 and your vertical line stays vertical out to 50, you found center shot. Not before.
And write the number down. The one your bow actually settled on, not the one off the chart. Because the day you change arrows, swap a rest, or restring it, you're starting over — and knowing your bow likes 25/32nds instead of 13/16ths saves you an hour next time.
The chart number is somebody's average. Your bow isn't average. Nothing is. The whole reason tuning takes a bench and not a ruler is that every rig is its own little argument between stiff sides and cam lean and the way you happen to grip the thing.
If you want the spine and FOC side squared away before you go chasing the rest — because half of "won't tune" problems are actually the wrong arrow, not the wrong center shot — run your build through The Forge first. Get the arrow right, then let walk-back tuning find where it wants to sit. In that order. Always.