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Bachetti et al. (2021) have recently claimed to measure the mass transferrate in the pulsing ULX system M82 X-2 by following the change of its orbitalperiod over 7 yr. We reiterate the known point that this method cannot give areliable result (or even necessarily predict the correct sign of long-termperiod change) without a far longer baseline (here $\gg 1000$~yr) or forsystems with a much higher long-term mass transfer rate ($\gg 10^{-4} \rmM_{\odot}/{\rm yr}$), if they exist. Applying the method of Bachetti et al.(2021) to measured orbital period derivatives predicts that the well-studiedquiescent X-ray transients XTEJ1118+480, A0620-00 should currently instead havesteady accretion discs and be bright X-ray sources, while Nova Muscae 1991should be still brighter (a ULX). But all three sources are observed to beextremely faint. We conclude that there is no evidence to support the high masstransfer rate that Bachetti et al. (2021) find for M82 X-2 as it is deducedfrom period noise not related to the binary evolution.

One for the Future: measuring the mass transfer rate in the ULX M82 X-2 by using orbital period changes will take millenia