Layout 3" 5" total station

It all depends upon what you are laying out. You are speaking of a difference of two seconds in the optimum case, maybe 4 seconds otherwise.

Also, realize that just because the label on the box says it's a 3 second instrument, that's not necessarily the result you are going to get.

After all, what is the tangent of 4 seconds, carried out over 100 meters?

Under ordinary circumstances, even a 10 second gun is adequate for most layout tasks, given multiple turnings.

After all, long before total station instruments, skyscrapers were erected using 30 second or even one minute transits and steel tapes.

Depends on how many times you turn your angles doesn't it?

Cowboy has it right. According to my calculator 5" at 100 meters is less than .01'. On a typical construction site does the average (or even better than average) surveyor do that good a work? And how many contractors come anywhere near that.

There are occasions that we have to do better, but I suspect angles are the least of your problems because the average TS specs start out at +/- .02 plus ppm for distances. Then we take shots on a prism 5' above ground on a prism pole with a dinky little circular bubble - which most of the time only the good Lord knows when it was checked. And if I'm on the prism pole it wobbles worse than my grandmother would have held it.

Not sure exactly what you mean by "greater", but I don't think you would be able to tell the difference if you used proper procedures.

There appears to be a belief in many engineering companies that 3" accuracy is the minimum standard in the choice/use of a total station.

Ignoring the potential propagation of error throughout the whole system, the DIN specs are pretty clear.

Replace "sets" with "horizon closure".
Or Kent will beat me.

I have had a 5" gun (Either Leica or Pentax) for the last 15 years.

Everything I have laid out for construction is still in place (to the best of my knowledge). I guess someone would have contacted me otherwise.

Too many variables to conclude that a 3 second gun is more accurate than a 5 second gun in the construction arena.

Every tool used must be in adjustment, layout rod needs to be accurate, ppm's need to be accurate, etc, etc.

So I say at a 100 meters, the guns should be identical enough that is does not matter (In the real world, anyway)

Randy

While the equipment today is much more precise and probably more accurate, I've laid out miles of roadway, footings and anchor bolts, structures up to 6 stories, and hundreds of manholes and catch basins using a 20 second transit. It all worked. That is NOT to say that one shouldn't use the best available, just that we should think about the needs of the site and what would be acceptable (both to you and the contractor). Those old transits didn't need batteries either (grin).

Andy

As stated it's a simple trig equation.

Too many today do not have a handle on accepted tolerance for the work being done. I have heard of surveyors worried about 0.05'staking rough grade. Same for locations doing a ALTA, it's a topo.

At the other end of the spectrum are the ones who slop in rough grade control points, then later on someone finds it and uses it to set building corners or a bridge.

Know what you are doing and how close it has to be. Watch the curb or storm drain installers and see how accurate they set their forms.

My son gets concerned on a topo survey when he checks his backsite at the end of a session and is off 15 sec. Not worth worrying about when your longest shot is 200ft.

Rule of thumb 1 min = .03ft in 100ft.