Thanks for the help joegrundman
I think I now understand most of how this works.
I am wanting to test the clicks on the RAOBF.
I have measured the info from map.
Range = 850m
Mastheight = 28.4
zoom is x1.5
Testing range.
Mast should be at
3.5 clicks but shows 4
I use the bottom right marker for zoom x1.5