How to do compression test

A customer with a 2012 KIA Soul 2.0L, 4-cylinder, aluminum block and head,  has come to your shop with suspected low compression in their engine. The customer also mentions the engine is missing on cylinders 3 & 4.

The customer askes your recommendation on how to diagnose their issues.

You suggest starting with a cylinder balance test.

Explain in your own words how to perform a cylinder balance test on this vehicle and how to interpret the results.

Idle speed in cylinders 1 & 2 drop 200rpm each

Idle speed changes very little when testing cylinders 3 & 4 (less than 25rpm)