I create a new diagram. I hope you all understand better.

by jwardana

Some 20 years ago as a teenage, my father gave me my first airgun with a scope. And then I faced my first problem using the scope (I'd used to open sight before this). I knew that if I zeroed the scope to certain distance (lets say 20 yards) then I had to aim higher for closer target and lower for longer one. But how high and low depends on how far the target is (which is very variable - and pardon my English, I am an Indonesian), and this is not easy (correct me if I'm wrong).
Then came this idea: why not set the zero to infinity?! It means that I had to set the cross off the scope sight as high as the distance between the scope and the barrel. In other word I set the line of sight parallel with the bullet's trajectory (I assume flat at certain range). With this technique, it is much easier for me to predict where to aim regardless the distance of the target.
Take a look at this diagram:
So let's say I want to aim at that medium sized rat, whose head is about 40mm (1.5") in diameter (help me predicting how high I have to aim), then I aim the cross 30mm or 1.2" higher (that's the distance between my scope and barrel) than the target (mouse head). Of course there always be tolerance. I say 5 to 10mm (for farther target) is acceptable.
I have practiced this for around 20 years. Many small and medium sized quarry had been gunned down with this technique.
Nowadays, after reading so many articles about airgun especially about zeroing telescopic sight, I've never seen someone who did the same as I did. I want to know whether there's someone who do the same as I did and I also asking for opinions about this technique.

Thanks, Jim. 20080505.