I need to know where to take measurements from on my gun to get the std dev(scope hight). Right now my gun is sighted in 4.5 high at 100 but at 300 its 11 high.I need my scope hight to see what my max distance zero will be at 2.5 at 100 sight in. its a sako trg 30-378 with sako high rings,5-15x50 bausch & lomb scope.

measure the diameter of the barrel shank and the scope at the same spot on the gun. divide each number in half. measure the distance between the two at that point. add these three figures and you will have the exact scope height from bore center.
woofer

I simplified the process by taking the windage cape off the scope and opening the bolt. Use a ruler or calipers to measure from the center of the windage adjustment to the firing pin hole. You should have acceptable accuracy for inputting your center line of scope and bore relation.

Woofers methiod is the most accurate (and correct) way
Quarterrounds way will be close, but high (he's measuring the hyptanuse(sp) not the side).
Another close and quick way is to measure from the stock line (normaly the centerline of the receiver/barrel) to the approxamite centerline of the scope.