I would rather buy a vacuum tool that removes all the air from the diff rather than some checker. Regular rebuilds cost less than one checker. Having several diffs built at different CTS, I personally see this as a vanity tool while it may provide consistency in theory with numbers, the best method is to rebuild as the data is presented in variables that often times are irrelevant. My point imho is that if you open a diff to top it off.. change the oil, if it is leaking replace bad seals, outdrive, and or, case I believe this will provide more consistency hard or soft. After all the engineers that developed the oil are in theory correct.