This product works as advertised. Note that this type of compression tester is a bit more difficult to use than the "press to snug" type, which requires one person to press firmly against the spark plug hole while someone else cranks the engine. This tester is the screw type I specifically wanted. Obviously reading each individual spark plug takes longer but has the benefit of being a one man operation and I think you get more accurate readings. This worked fine for me.
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