So I had a fellow worker explain a leveling technique I never heard of. Say you want to run a level circuit and close back on your starting point. Instead of running the circuit one way and then running it back, you have two turns on each setup and only run the circuit one way.
You would say set one turn with a screw driver, and then set a second turn next to it on say a hatchet. Then you read both rods from the setup and move ahead. It was explained to me that this was the same as running the circuit down and back. I've never heard of this before and in my mind its not the same running a closed loop but I'm always open for new ideas. Opinions?
So you're running 2 separate forward runs and theoretically they would provide a check for each other instead of closing back. Might be crazy enough to work, but keeping 2 books sounds like more work than it may be worth.
Elephino, I havent used a level in years.
I have done it that way before for long routes. Special care needs to be taken to try and keep the numbers for the close stations to be different. Best if they are on a different foot part of the rod or you may make the same mistake on each reading. For instance, reading 4.98 and 4.92 on one pair of backsights when they are really 3.98 and 3.92. You won't pick up the error in your closure at the end but it will be there...
It's a great technique if you don't want to have to trek the route twice (nasty woods, swampy, brutal cold), and accomplishes the same thing. Two independent measurements for each station/setup. The instrument doesn't have to travel a physical loop to obtain the same data.
I used do this with traverses all the time (when I was actually in the field more often), and it goes especially fast with a 3-person crew. Get set up, turn your sets, break setup for instrument and BS/FS, turn another round of sets, then move up and repeat. You then have redundant measurements at each station. Run LSA to get final coordinates.
If it is absolutely required by the project I will compute a closure from the observations, but with redundant observations at each station (out-and-back) least squares is the way to go.
I have seen this technique before and it fails if the stations are not broken in height significantly, as said above. Basically if the wrong foot is read once, it will be read that way again, more than likely. We read electronically now, so, we aren't really subject to that. That concern may have gone the way of the plumb bob.