You ever notice how the really good guys can just look at a load and know? I had a foreman back in the day who would grab a handful of mix and squeeze it, then just nod or shake his head. Took me a while to figure out what he was feeling for, but he was almost always right about whether the slump was in range. Chuck's trick with listening makes sense too, you can hear the water sloshing different versus a drier mix rumbling around in there. The key is you gotta get your ear calibrated against the actual slump test results until you can trust what you're sensing.

Man, that's a lucky find. The thing about blogs like that is they often have comments sections where old timers chime in with fixes you won't find in any manual. I've seen people post photos of their grandfather's modified tools for specific machine repairs, stuff you'd never think of. Did you check if he had a section on cleaning old grease without hurting the paint? That's usually the trick that saves a machine from the scrap pile.