Why don't they use a machine to call balls and strikes?

[smitch124]

Well the strike zone is actually different for every batter. Some crouch more than others, so defining the strike zone is difficult, but not impossible. I think it is a long way down the road, but may happen at some point.

[Boner_18]

Just simply define it as average player measurements and recalculate it annually. Its simple and accurate and it actually stops "gaming" of the strike zone eg Eddie Gaedel.