I've suggested several times to @Sandor Szekely, that it would be far better to use a fixed point (like a headland) in the middle and end, rather than a boat. Then accurate measurements could be taken. But he prefers the boat.
The calculations are a little complex, however you don't need them. You just need to show that the measurements do not lay on a straight line. The Wallace experiment demonstrates this with three points. Since Sandor is using a boat I've suggested that he takes as many measurements as possible so the curve will show through the noise.
The Wallace setup at 3 miles would be the same as the orange line here:
With the laser tilted down at 2 feet per mile.
Sandor has indicated he's going to do something more like the purple line (0.66 feet per mile, by leveling the laser at 1 mile. This will give a greater (and more apparent) deviation at 3 miles than the Wallace method of leveling at 3 miles, and then going back to the center.
This is VERY IMPORTANT:
Mick : "You just need to show that the measurements do not lay on a straight line."
Exactly! And in my opinion my type of slope corrected level measurement will give a more definite result than the Wallace type measurement. I am ready to do both, and I can find a target in position B to level the laser as Wallace did.
for example here: