thermometers
Dr. Richard Henry in his book "Controls in Black and White . . ." has a section on thermometers he tested, including some very expensive 'laboratory grade' instruments; he found them appalingly (my adjective) inconsistent, considering their expense and claims. I have a Kodak Process thermometer I purchased some years ago which guarantees a certain accuracy, apparently not to be believed. I paid close to $100 about 25 years ago (a princely sum then) and it has worked fine ever since. I really have no idea how 'accurate' it is in comparison to some standard or other, but I trust its consistency. So since all my processing is measured with this thermometer it is at least consistent. Which is what counts, I think'
If doing it again I would save some money and buy a thermometer that is consistent. I think for our purposes, consistency is much more important than absoloute accuracy