As a home engineer that rebuilds lathes, mills and other highly accurate machines down to the micron level (1/1000th mm) the importance of having everything at

As a home engineer that rebuilds lathes, mills and other highly accurate machines down to the micron level (1/1000th mm) the importance of having everything at the same temperature when rebuilding is of the utmost importance. All my test kit; block gauges, micrometers, 300kg surface plate, engineers levels, sine bars etc are calibrated at 20'c (the industry standard) .. one of the best ways to see the effect temperature has on accuracy is to warm one side of an engineers level in your hand then place it on a surface and watch the bubble move as the temperature equalizes.