Am supprised that so many didn't know what it was.......
Its my version of an ACI (Angle Cosine Indicator) and is calibrated in the cosine of the angle 90 ldegrees being one.
When one is shooting a long ways and either uphill or down hill you multiply the range finder distance by the cosine of the angle to get effective distance the shot has to travel.
I try to center the target in the center of the scope then see what number the ballistic tip it pointing at. Then multiply the range finder distance by that number.
Where I was going to make the shot the values were either .98 or .94.
Son did all the shooting that day and the shots were about 100 yds thus the gizmo was not to useful, as are most of my inventions.
For anything under 500 yds and your target is deer or elk the cosine doesn't make much difference. For loooooong shot its a deal breaker.
When I get really serious, I'll purchace a scope or rifle mounted ACI. The wind blows that bt around a bit.
