Yes, that's exactly how you're supposed to check. But there is the "manual" way as well.
And that's to adjust the rod out to the point that it bottoms out on the back of the piston just before the master cylinder mounting flange touches the booster face, then you adjust the rod back in to the point that you can mate the two items together before the piston touches the rod.
A 1/16" gap is too big. Should be less than half of that if I remember.
I used to use 1/64" as my guide, but there is an official specification in the book and someone posted it up here last year so it should be around.
I'll see if I can find what Chilton's or Haynes lists, but as long as you don't have the rod touching the piston you're gettin' close.
The tight gap is at least partly because the pedal ratio could be at least 6:1 which means that a 1/8" gap would equate to an extra 3/4" of pedal travel before the piston even starts to move.
An 8:1 pedal ratio would give you a full inch at the pedal before the initial brake travel starts. Too much gap and you could end up with perfectly good stopping brakes, but a pedal that's almost at the floor before you stop!
So less is better, up to a point.
I'm sure you'll find the exact spec. And you can use the touchy-feely method I described and get it pretty close. But the measure-it-with-the-proper-tools method is what gets you right on the money as far as the factory spec is concerned.
Paul