Are these just guesstimates based on page count and average usage? And is it fine tuned a bit by print quality and paper type? I figure it's the common way for most brands.
And, btw, I use clear refillables so I can also check, and monitor more accurately
I did see a Brother that I think had floats or something that could actually give more accurate readings.
Reminds me of my old Peugeot 505 that had a float in the sump to give an oil volume reading. Good feature, makes sense.