A quantity added to the time of the chronographic signal of a stellar transit observed using an electrically recording, impersonal micrometer, to allow for the time required for the contact spring to cross half the width of a contact strip in the head of the micrometer. In order to ensure a satisfactory signal, the contact strips are given an appreciable width. As the micrometer wire travels from different sides of the instrument at upper and lower culminations, and also before and after reversal of the instrument, the contact spring produces a signal sometimes from one edge of a contact strip and sometimes from the other. The contact correction is intended to produce the time that would have been recorded if the electrical signal had occurred only when the contact spring crossed the middle of the contact strip.