  A calculus based on pointer-mark coincidences is proposed to define, in a
mathematically rigorous way, measurements of space and time intervals. The
connection between such measurements in different inertial frames according to
the Galilean or Lorentz transformations is then studied using new, simple, and
practical clock synchronisation procedures. It is found that measured length
intervals are Lorentz invariant, whereas moving clocks show a universal time
dilatation effect. The `relativistic length contraction' and `relativity of
simultaneity' effects of conventional special relativity theory are shown to be
the consequence of calculational error. Two derivations of the Lorentz
transformation from simple postulates, without reference to electrodynamics or
any other dynamical theory, are reviewed in an appendix.
