A sign error in the Minkowski space-time plot and its consequences

A sign error in an angle while drawing the original Minkowski plot has persisted for a century in text books and the pedagogical literature. When it is corrected, the `length contraction' effect derived from the geometry of the plot disappears. It is also shown how the `relativity of simultaneity' effect that has been derived from the plot results from a lack of correspondence between certain geometrical projections on the plot and the properties of the physical system --two spatially separated and synchronised clocks in a common inertial frame-- that they are purported to describe.