Undercarriage
Measured, not eyeballed.
Grouser height against new spec, link height, bushing condition and rotation, roller and idler flange and tread wear, sprocket tooth profile — hooked teeth mean the chain has stretched. Every item is expressed as percentage of life remaining, never as “good” or “worn”. On a tracked machine this is usually the largest single deferred cost, and it is the item most often guessed at.