Chronometer

Also known as Marine Chronometer

This is an example of a marine chronometer, made by Victor Kullberg, which is in the Royal Museums Greenwich. Marine chronometers were used to keep accurate Greenwich mean time at sea. In conjunction with a sextant to observe local noon time, this allowed the determination of longitude (defined relative to the zero longitude at Greenwich).

During the latter part of the 19th century, ships' chronometers would have been brought to Bidston Observatory for setting accurate Greenwich Mean Time and rating. Rating included checking the temperature response of the chronometer using the 'hotbox' developed by the Obsevatory's Director John Hartnup.