greetings all: i am considering purchasing a differential compression tester. the tester that most a&p mechanics use is an automotive type? best for me to buy a tester with the .030" orifice? or do the automotive testers,such as Mac and Snap-On, already have the .030" orifice? continental engines is the only engine manufacturer to specify the orifice size? i would like a tester that i could also use on auto engines.what to buy? ....thank you....