An instrument for producing a graphical record of the time, shown by a clock or other device, at which an event occurs. In use, a chronograph produces a double record. The first is made by the associated clock and forms a continuous line with significant marks indicating periodic beats of the clock. The second is made by some external agency, human or mechanical, and records the occurrence of an event or series of events (which may be the beats produced by a second clock). The times, as shown by the clock, of such occurrences are read from the record made by the chronograph. In observations for time and longitude, the occurrences of stellar observations are recorded on the chronograph either manually by pressing a key at the instant a star is bisected by a line of the reticle of the telescope used in the observing, or automatically by keeping a star bisected by a movable wire as it travels across the field of view. (SEE transit micrometer). In determining longitudes, the chronograph also records the time at which signals are received from the station of known longitude. The chronograph has been replaced, by many organizations, by equipment which records digitally, on magnetic tape, the time at which an event occurs.