“This handy little instrument will be found very useful for Cyclists and others, the roads and distances on a map being easily measured and the distances calculated”

This month’s map measure is a sweet little item made by Francis Barker & Son. The business was originally established as F. Barker at 12 Clerkenwell Road, London in 1848. They made a wide range of precision instruments including compasses and sundials. The Rotameter, or rota-meter, was just one of a wide range of products offered by the company.

The Rotameter map measurer appears in Barker’s 1885 to 1907 catalogues and was probably available to buy until circa 1915. It was not listed in the 1926 catalogue. It could be purchased in a variety of finishes. The cheapest was the nickel-plated measure at just two shillings and sixpence. The 1885 catalogue offered:

By 1907 the cost of the 15-carat gold version (without compass) had risen to £2 and there was also the option of 18-carat or 10-carat gold. Gilt, nickel, bronze silver or gold finished versions were available in 1908.

You may come across other examples of this ‘charm map measurer‘ that appear to have been made by other manufacturers but, other than those made by E.R. Morris of Birmingham, they were all made by F. Barker & Son. It is small, weighing 15g and measuring just 26mm diameter, and is designed to hang from a watch chain.

There was also a larger version of the Rotameter offered in 1908. Another option had a compass on the reverse side and later options exchanged the pendant ring for a bone handle or propelling pencil. The simple and small design leans heavily on the measurer formerly offered by Morris Instruments. Three Points of the Compass covered that measurer in another post.

The large blued hand rotates forward in increments of an eighth of an inch, with inches shown on the dial. One complete revolution indicated one foot (12 inches) measured. Each complete turn of the dial also moves the small hand forward one foot with the ability to measure up to 25 feet. Increments of five, ten, fifteen, twenty and twenty-five feet are shown. This little measure was also sold with a different paper dial that included tiny figures indicating each individual foot up to 25. These were so cramped that this simpler face is easier to read.

The Rotameter shown here is the simpler, cheaper version with no compass in the rear. This example has a plain glass face and plain unmarked back. An alternative later offered by Barker was for a ‘pebble’ crystal front, this would slightly magnify the dial behind. The smooth wheel protruding from the bottom is simply run along a map route and the needle correspondingly rotates around the dial indicating inches and feet covered on a map, or any other object for that matter. Knowing the scale of the map enabled a reasonably accurate distance to be determined.

It is an uncommon and remarkable survivor. These normally had a tough and short life yet despite a well-worn case my example still performs faultlessly. Testament to a good, simple and well-made design.

Three Points of the Compass has looked at a few more Map Measurers in detail. Links to these can be found here.