Thanks for the input Ken

Does this proceedure pretty much guarantee that my model will still be in range when flying at a distance of ...... having trouble now relating "percived distance on the field" to actual feet !! - lets say a distance where, with care, and my average eyesight, I can still make out the full shape of the model and see what direction / attitude it is in. (The Sparky 400 is about 50" span, with full fusalage and tail feathers)