https://measure.infopop.cc/eve/...69510622/m/620101968
This weekend I returned to that course to test out my EDM. I placed my targets at the two endpoints. However, I discovered that the nail was missing from my south endpoint. My thick white line was still there, and I placed my target at the south edge of this line. I then placed my mounted EDM at a point near the middle of the targets and took several measurements.
Since my last test of my EDM I changed a couple things. First, inspired by Mike Sandford's use of reflectors as targets, I put reflective tape on my targets.
This isn't necessary for the EDM to receive the reflected laser and make a measurement, but it is helpful in assuring that it is targeting the right thing. Usually with the naked eye at 150m, and always with a small pair of binoculars, the laser dot can be seen on the target before taking a measurement.
The second change I made was that rather than spinning the mount as described before, I simply lift up the whole apparatus and turn it 180 degrees. For both measurements I line up the back of the EDM with a piece of tape on the ground. I changed this because I found that spinning the mount did not give a consistent offset from the back of the EDM.
My four measurements are shown below.
After seeing the measurements were about 10cm longer than 300m, I decided to remeasure the cal course with a steel tape. Starting at the south edge of the white line at the south target (which is where I had placed my target) I got 300.085m.
So the average of all four EDM measurements was 16mm different from the steel tape measurement. And the worst case for averaging only two EDM measurements was 20mm different from the steel tape measurement.