  This brings us to the problem of measurement. Normally when we measure an interval we believe we are indeed measuring space or time. However, measurement relies upon comparison. This was important for Mach: we do not measure ‘space’, but rather we compare our spatial sensations. All measurement requires the use of a standard, and since any standard we pick is of the same nature as the thing we are measuring, we do not truly measure anything (if by this we mean an absolute measurement):