instrument used to check compression pressure. Typically, the dial
on a compression gauge reads in both pounds per square inch (psi)
and kilopascals (kPa), with a range of about 0 to 300 psi or 0 to
2,100 kPa. There are two main types of compression gauge. The push-in
type has a short stem with a tapered rubber tip that fits any size
spark plug hole. To measure the compression pressure, the rubber
tip is pushed into a vacated spark plug hole and held tightly in
placed while the engine is cranked through a few compression cycles.
The screw-in gauge has a long, flexible hose with a threaded adapter.
It has a couple of advantages over the push-in type. First, the
hose can reach into places that otherwise might be inaccessible.
Second, because the threaded adapter screws securely into place
it tends to give more accurate readings.