This month’s measure is a navigators divider, sometimes called divider calipers, made by W&HC. It is such a simple instrument, little description is required.
The two sharp stainless steel points are used for measuring distances on a nautical chart by transferring the gap between the pointed legs to or from a scale. Using the dividers and the latitude scale on a nautical chart, it is possible to measure a distance in nautical miles. The upper part of the legs and the hinge are made from solid brass in a semi-circular form. This shape enables the user to alter the gap distance using only one hand, hence this type being known as a ‘one hand divider’. The selected gap in the tips is maintained by friction at the pivot hinge, the large slotted screw can be tightened if necessary. The maximum width the calipers can be opened to is eight inches (203mm) but would normally be used at far less a division.
Navigation dividers come in various lengths. The English-made dividers shown here are eight inches long and have a brass head with 18/8 stainless steel legs. The first number- 18, refers to the amount of chromium present and the second represents the amount of nickel. So, the 300 series stainless steel on these calipers has 18% chromium and 8% nickel. The all metal construction means these are quite weighty at 87g.
My pair of dividers have had a life. They are dinged, worn, scratched and tarnished. Testament to considerable use and far removed from the shiny brass dividers so frequently seen elsewhere. Yet such is their simplicity that they still work. No doubt GPS has decreased their usefulness in modern times but knowledge on the use of navigation dividers is still a requirement for those in charge of sea going vessels.
They are a simple tool and similar instruments have been used by navigators for centuries. I have included here an image from the Bianco World Map of 1436. Note that sailor and cartographer Andrea Bianco has included a cherub with easily recognised navigation divider on one of his drawings.
These dividers are quick and easy to ‘walk’ across a map or chart and surprisingly accurate. These were an essential tool for the sailor and my pair have a family connection. These were used by my uncle in the 1970s and ’80s in his role as Tug Master.
There is almost nothing I can add to this scant description and am frustrated in not being able to expand on the maker. I know nothing of W&HC and welcome any additional information.
Three Points of the Compass has looked at a few more Map Measurers in detail. Links to these can be found here.