Igneous Rock is formed when a magma cools underground and crystallizes or when it erupts unto the surface of the ground, cools and crystallizes. Magma that erupts onto the surface is called lava. When magma cools slowly underground the crystals are large enough to see.
Readings for compression tests usually vary between 175 to 250 PSI (Pounds per Square Inch). A higher reading generally indicates better engine performance; however you should check your vehicle manual to find out what the ideal reading should be for your vehicle.
6. Put the engine compression gauge into the first cylinder's spark plug hole (this is the hole that is nearest to the drive belt). Don't use any additional tools to tighten the compression gauge, you should only use hand force.1  7 Edit step. Turn off the car engine and allow the engine to cool if you have recently taken your car for a drive. 2  If the engine is hot, it should be given approximately 1 hour to rest before you do a compression test on it.