Reloading .303 British : Digital scales

They can be influenced by things like electrical noise from things like florescent lights.

I still have my PACT model 1 from the stone age.

It works fine, but I am very alert to electrical "noise" & have intermittently checked it with a full set of check weights, not just the 2 supplied.

Back in my lab days I learned working a Mass Spectrometer & an Atomic Absorption Analysis unit that the more calibration points you set up the more stable & accurate the instrument was because the calibration curves were smoother.

Maybe that's why the PACT works so well it uses a 5-point calibration system?