NavList:

Tony,

I think Frank is refering to collimation uncertainty in both the calibration and observation process and that the degree of uncertainty increases with the altitude of the reflected body image. I find it very difficult to use the Bris in the fingers to find the low point through fiddling. The pitch,yaw, and roll axis needs to be duplicated in both calibrating and observing to get repeatability and accuracy. This is why I am using a DSLR camera as a platform. Not for taking pictures but rather to lock in the pitch, yaw, and roll axis for both calibration and observing. The camera reticle also does a great job of centering the reflected image and horizon for further repeatable consistency. No matter the mechanics the DSLR observations out perform hand held observations on intercept distances from a GPS position at the sea shore. If used on the water even more uncertainty is added due to vessel motion and height of eye change going from swell top to trough and back. Calibration should not be done while underway on the water.

Greg Rudzinski 34° 10' N  119° 14' W