[DELurker]

When I worked on our distance calculations (over the summer), the first thing I did was get the actual horizontal and vertical FOV angles. The FOV angle in the manual is usually the diagonal FOV, which is useful to almost nobody. So, my first recommendation would be to measure your camera's specifics. We counted the number of bricks visible on the exterior wall and then measured them.

Some of the other tricks we used are not applicable this year. However, if you got the smallest outer bounding box that held the tape and the biggest inner bounding box that fit in the tape, you could average the heights and compare that to 16" (inner box + 2*(half tape width). This should counteract any parallax from not being centered on the target.

Could you post a copy of your code? Someone might be able to find why you're getting numbers that are so far off. You should be able to calculate within 2-3" or so.