This chronograph was manufactured by the watch and clockmaker Krille of Altona, then Denmark around 1870. The clockwork movement is weight-driven and its running speed is governed by an adjustable fly. As the recording barrel is rotated by the movement, differential gearing moves it longitudinally along its arbor. A piece of paper would be wrapped around the barrel and inscribed with lines by two pens as the barrel rotated and advanced along a screw. Two armatures (only one of which remains) held the pens so that when two corresponding electromagnets were activated the lines being traced on the barrel would shift right or left. One electromagnet was connected to the personal equation machine so that the pen inscribed the passing of artificial stars on the drum. The other electromagnet was controlled by an observer sitting at the transit circle so that the pen registered the time of an observation alongside the instant the artificial star passed the meridian.
This chronograph was used in the personal equation studies conducted at the Royal Observatory with the personal equation machine in June 1887. Remnants of two labels can still be seen at the terminals where the wires from the personal equation machine and the transit circle connected to the electromagnets. The Krille Chronograph was used from 1887, replacing the Airy Barrel Chronograph (installed 1854), which was normally used in the observation of transits. Whereas the Barrel Chronograph recorded observations through a series of punctures, Krille’s recorded a continuous line so that the duration of a contact could also be measured.
The personal equation experiments were intended to calculate the reaction time or personality of individual observers. An apparatus called the personal equation machine which projected the image of moving stars was placed at the north end of the Airy Transit Circle (1851) and observations were made as usual by pressing a contact when a star crossed the wires of the transit instrument. This registered the time of observation on the chronograph against an automated contact within the personal equation machine which registered the moment when the artificial star crossed the meridian. Before beginning a series of observations the observer would register the seconds impulses of the transit clock (Hardy) creating a time scale on the chronograph. The results of individual observers were compared and published each year in the Greenwich Observations.
By 1912 the Krille chronograph served in the Time Department where it registered return time signals, possibly from the Deal time-ball.