 Thus, this footnote in his masterly Relativity and Geometry suggests that, for Torretti, we are misled into using different units for mass and energy merely because of how we perceive space and time. As we have seen, one can use the same units for mass and energy by adopting the convention Torretti himself uses of selecting units in which \(c = 1\) (pp. 88–89). However, it may be useful to remember that merely using the same units for spatial and temporal intervals does not entail that space and time are treated “on a par” in special relativity; they are not, as is evident from the signature of the Minkwoski metric.