You make think this funny, but I understood when Bob gave the estimate today: You've got a good starter "it smell good".
this is called organoleptic testing and still could be found as a valid procedure in some standardized metrological procedures.
For example, you could try to take up sniffing various motor oils - you will see what I mean. A lot of the syn blend elixirs are gimmicks, they reek sulfur.. even more than some good, old mineral oils. PQIA stopped publishing the sulfur content numbers recently: it was too obvious that all the fake syn this, Polonium that is a marketing nonsense. Same goes for the ATF concoctions. The same ATF from different vendors will smell differently. [it may be a good things, when some extreme pressure lubricants are sulfur stinkers, though, e.g. gear oils have EP additives with funny odors]
So, your Old Master goes by experience and observation - a Method Man, Scientific Method that is