A leakdown tester is a where the each cylinder is pressurized with air 100+ lbs. The engine is not running and a strong person holds a breaker bar on the crank. The measured rate of air going past rings and valves at TDC will tell you the condition of an engine. By far a better test than simple compression. It is the only way to test a two stroke. I have seen 2 stroke engines with good compression, but a lot of leakdown that ran like garbage they were so worn out. The unit is not that expensive. Requires an air compressor source.