IThe reality of the math and physics is very complicated yes. But to get a "feel" for it in a game, you can "absrtract" it to a degree.
The link shows charts that have also been made by excel. The particular charts are used cause they start at dead center which is used to represent the actual vehicle. They show potential penetration but not shatter gap.
I use an average penetration in millimeters. While many counter that no two shots are exactly same penetration. cutting it off at an average saves times and is still plenty accurate to represent the weapons abilities. I am big with optional rules though and add optional rules allowing for variance of penetration.
IN game terms shatter gap is simple. Where it is known to occur like that of the American 76mm AT gun the ranges and targets that cause the effect are noted. Shots by the weapon against those targets at those ranges are ineffective.
Example. a M-18 is firing at a Panther from 600 meters away. If this was listed as a shatter gap issue, then the shot would be ineffective.
So the rule amounts to nothing more then a notation on the M-18 data card that shots against certain Tanks at certain ranges will be ineffective. The shatter gap is represented by the players don't need to know any math or physics.
paints 
