Well, it all depends wether the fluctuation is in the high end or the low end, for example: If you are reading a density of 1.80 and it varies +/- .03 then you are within the 1% variation densitometers usually have, but if you are reading a density of 0.15 and it varies by .03 then you are screwed! I also had the same problem, an ebay guy sold me an ESECO speedmaster supposedly in excellent condition, and the piece of ^%$^ would not zero and/or hold calibration, so now I know why he sold this unit.(posted 8430 days ago)