CountryByNet.com Forums :: Re: Using transit to set corner posts square!!!

Yeah, that would give you a square corner to "some tolerance". The term "exactly 90 degrees" is the caveat. Using that method, I've used my transit to determine a survey stake location that had been moved by a neighbor (long story). I then had it verified by a licensed surveyor and I was within a couple of inches of where they set it. I've also laid out rough building corners on batter boards for sitework using a transit (similar technique as you and Egon describe). When checking against diagonals, invariably 1 (or 2) of the strings must be moved on the batter boards by a small amount. As Egon indicates, it's an iterative process.

Variability comes from the resolution of the transit (expensive vs cheap) and how well you can set them as opposed to someone else, (operator variation) and the distance over which the measurement is taken (1% error at a longer distance may be significant to your project).

But, to answer your question, yeah, it's pretty fast and I would certainly have mine setup when erecting the framework of a building, then check as previously described. I'm a big proponent of "measure twice, cut once" so I tend to double-check & triple-check everything.

(It's better than using a carpenter's square to check the 90 degree angle. A 1/16" error along the 2' length of a carpenter's square will extrapolate to an error of 1.25" error along a 40 ft wall.)

Also, I only trust a 3x4x5 for "final" verification on "hard" surfaces (like a roof or floor) where the legs of the measurement don't move (i.e. string) and you can make solid clean marks. But it's ok to determine where to set the batter boards using string.

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