A method of measuring the time at which a stellar image crosses a particular line in a reticle, by counting off the seconds or half seconds to oneself while observing the passage. Counting is started by looking at the chronometer and counting in cadence with its ticks. Attention is then diverted to the telescope but counting is continued. The interval from the tick just before crossing to the moment of crossing is estimated, and the times of the ticks themselves remembered. The time of crossing is calculated from these values.