I've been trying to work on a simplified calibration method. Yesterday I tried the method out in my backyard and I got an error of 0.35 degrees and a max error of 1.05 degrees.

Today I tried the method out in my backyard and got an error of 0.49 degrees and a max error of 2.24 degrees. The differences physically were that I had moved about 3 feet (in my backyard), had left a tablet sitting ~1 foot away, had a tripod 3 feet away, and had my keys in my right pocket during the second attempt. I also went a LOT faster the second time. Maybe I should have been more careful. However, I'm guessing that those aren't enough to cause this much of a difference. But I don't really know.

I'd like to try to fine-tune this simplified method. It makes it a lot easier for people to calibrate. That should make it less likely for people to skip calibration, especially when they don't have a local compass course set up.

I uploaded a youTube showing the method because I believe in scientific evaluation. If anyone is able I'd be interested to hear if they can repeat my results.

https://youtu.be/IYAKCc9ZCJ0

I plan to try this in a cave next time I can (I don't get into caves often while working and doing an executive masters). I'd like to try this out in a high end compass course, but I won't be able to do that and compare my results in the near future.

Here's the basic method:

Equipment: DistoX2, 8" plastic square (triangular with 45 degree edge), tablet with topoDroid app (for post processing only), a flat surace (I used plexiglass).

Setup: Find a surface that is fairly level. Use your flat object (plexiglass or other) and make sure the surface is stable. Use the bottom wide edge of the plastic square to form an edge on your flat surface that you can butt the distox up against. Put the disto into calibration mode with no calibration shots saved. Press down on the square and keep pressure in order to keep it from moving.

Up/Down shots: Place the disto on the flat surface facing up. Push the disto up against the square so that one edge of the disto is flat against the square. Take a calibration shot. Rotate the disto 90 degrees around the laser direction (still facing up). Repeat until 4 shots complete with disto rotated each 90 degree turn while butted up against square. Point disto down and repeat.

N/S/E/W shots: Face the disto in your first direction (North for this description). Repeat the same steps as in Up/Down except make sure that the disto faces north for all 4 shots. You will have to turn the disto face-down in order to complete this. In order to get the face-down shot, first press the timer button on the disto, then press the shot button, then put the disto in place to take the shot making sure it is oriented and flush with the square before the timer completes. Repeat for S/E/W directions.

Angled shots: Set the square upright standing on its wider edge. position it so that it is at a 45 degree angle (compass directions) from it's orientation during the last set of instructions. Line the disto along the edge facing 45 degrees (clino directions) facing upwards. Take 4 shots while rotating the disto 90 degrees around the laser path each time. Then turn the compass so it is pointing down along the 45 degree (clino directions) edge and repeat. Next, you have to turn the square so that it is facing in a new compass direction by turning it 90 degrees. Then repeat the shots up along the edge and down along the edge. You will turn the square 3 times and shoot 8 sets of angled shots total.

Use the tablet or your PDA to download the 56 calibration shots from the disto and calculate the calibration co-efficients and errors.

For any confusion, see my youTube video.

Click to expand...

Adam, I think you might be over complicating this calibration thing.
At the moment all I do is go to a place just inside the entrance of a cave we are currently resurveying. I use the same spot as it works better/easier/quicker when you get a bit more familiar with that location. I have a stick which I ram into a crack in the floor the end of which then becomes my survey reference point. The stick is quite sturdy and does not wobble around. I then do the 56 readings making sure the point on the rear of the case opposite the laser stays on the end of the stick. The directions I point the Disto are a little random this is so I can use  rock features to aim the laser at and not forget what I was using whilst turning the Disto and have to start again but I roughly follow Beat's instructions. The down shots I offset the Disto from the stick top but am really careful to use the same rotational axis whilst doing the four measurements.
I have one of those Disto's that need the NL correction and when applied I usually get a .24-.26 delta. A rotation test will give me an error of <1 degree which works fine for me. Without The NL correction I can't get less than .52.
I too have thought about devices to help with the calibration and have even designed a fancy jig but in reality it's too much faff especially when the method above works fine and it only takes 10mins or so to complete.
One thing that might help is a pointy extension from the rear of the case on the laser axis. This could be made from aluminum and mounted to the case using the brass mounting thread on the base of the Disto. I think the Disto can be corrected for the point offset which will probably be 30mm or so. It would make keeping the laser on the same axis easier when rotating.
I watched your video, and I would imagine your environment would compromise your readings as may things such as your ring depending what its made of, also what about any rivets in your jeans if you get close enough. I did some trials regarding what personal kit effects the Disto and the results varied quite a bit. I would do some tests yourself to get a feel for this.
One more thing, Your method may fail because the laser axis is not always parallel to the Disto case. I would check this if I were you I suspect each unit varies a little. Thanks Dave Clucas for pointing this out a while back.
At the beginning I struggled a bit with calibration but now wonder what all the fuss was about. Keep it as simple as possible and it will work that's my advice.

Nick.

Yeah. I think my biggest problem has been finding a place to calibrate. Last time I couldn't get a good calibration in my cave. There wasn't a great room and I didn't have a stick or any way to prop it up. I tried twice. So I ended up giving up and using a Suunto. I either need to make sure I have a cave chamber I can successfully do this in and a stick I can use, or I need a simple method.

Also, I'm trying to get others to work on this survey when I'm not there. Hence me trying to make a standard process.

Thanks for the pointer about the ring. It's supposed to be tungsten carbide, but i can't guarantee there isn't any cobalt in there.

Adam