The clock rates at event q are equal (l^A_q = l^B_q) if and only if the electromagnetic field tensor F_jk(x) vanishes.

Suppose physical spacetime corresponds to a Weyl geometry. Then two identical clocks \(A\) and \(B\) at an event \(p\) with a common unit of time, that is, a timelike vector of given length \(l_{p}\), which are separated and moved along different world lines to an event \(q\), will not only differ with respect to the elapsed time (first clock effect (i.e., relativistic effect)), but in general the clocks will differ with respect to their common unit of time (rate of ticking) at \(q\) (secon