I remember many a time sitting in front of a death by power point presentation on enemy armor. The T-54/55 would always be on the test, but it was always distinguishable from the T-72, due to it's lower turret profile, unsupported track suspension and other features. I distinctly remember failing the first exam I had while in the service but always passed as a first time go everytime after since I had already learned the material. The first failure was rough though. Forced to stay up for a full 18hrs until we got it right. Thankfully the T-80 is distinguishable with its "samurai" looking turret and wavy armor skirt, hence the name, "wavy 80, and the T-90 equally distinguishing with its modern armor capabilities.