Hint No. 6
Watch out for your incubator temperature!
Are you familiar with this problem? When utilizing several incubator shakers in parallel, your results are not comparable despite using the same shaking
speed and diameter. This may be due to temperature differences. Incubator temperatures varying a few °C may have considerable influence on the growth
behavior of cells and hence on your data.
Growth rates of Escherichia coli at different temperatures
(S.L. Herendeen, R.A. van Bogelen, F.C. Neidhardt, Journal of Bacteriology (1979), Vol. 139 (1), pp 185-194).
Solution: Determine the temperature in your incubators with the same certified, external thermometer. With the appropriate instruments
you may even record temperature profiles in each incubator chamber over a longer period. Deviations of several °C are not uncommon and may be the cause
of your strange results