The Bygrave slide rule is a mechanical computational device that is used in navigation for determining distances and angles. It works by using two rulers that slide past each other and allow sailors to perform calculations by matching various scales on the device. Synonyms for this piece of equipment could include navigational slide rule, navigational rule or simply slide rule. Other terms like navigational instrument, angle computing tool or distance calculator may also be used. Despite the advance of digital technology, some navigators still prefer to use traditional tools like slide rules for their accuracy and ease of use.