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Map measurer of the month: The Roller Rule- “The Pencil with a Brain”

The Roller Rule was invented by John Hoe Morehead of Clarkdale, Arizona. This combination propelling pencil and measure was used by thousands of Americans as not only a general measuring device, it also found favour when used with inch scale maps. This “measuring attachment for pencils” received U.S. Patent No. 1599780 on 14 September 1926.

The Roller Rule
The Roller Rule

“In a device of the character described, an elongated supporting member including a threaded element, said member further including a graduated portion, a pointer movable longitudinally along said supporting member and a roller threadedly engaged upon said threaded element and operatively engaging the pointer whereby the latter will be moved longitudinaly upon rotation of the former”

Description of Roller Rule mechanism in U.S. Patent No. 1599780

The desciption accompanying the patent application seems almost impenetrable. But what is being decribed is the outer tube of a mechanical pencil fitted with a central screw shaft. The inner shaft is turned by rolling an outer wheel and as the shaft rotates, it moves a pointer up or down a window in the side of the tube.

Use as a pencil
Use as a pencil
Use as a measurer
Use as a measurer

The metal and plastic measure is a beauty. It is quite chunky in the hand but not as bulbous as a fountain pen. Black and gold. Measurement indicators are properly engraved and painted cream. Use of the measurer is immediately intuitive. Held normally, it is a propelling pencil, inverted and held in the same manner, it is a measuring device. Measurement of lines, be they on a map, or whatever else, is achieved by rolling the end-cap, fitted with a grippy rubber tyre around its circumference, along whatever requires measuring. The distance the wheel travels is indicated in inches along the window in the length of the pencil’s shaft. This window indicates from 0-36 in marked two inch increments with unmarked inch increments between these.

36 inches of measurement, in eighth of an inch increments, are shown on the side of the Roller Rule
The potential for 36 inches of measurement is indicated, in eighth of an inch increments, on the side of the Roller Rule
Measuring with the Roller Rule by rolling rubber tyre along map line
Measuring with the Roller Rule by rolling rubber tyre along map line, this rotates the inner screw shaft and moves the marker along the measuring scale

The pocket clip on the Roller Rule has the only writing, beside that for measuring, found anywhere on the pencil/measurer. This indicates that it has been patented in the USA as well as proudly showing its name.

Despite receiving its patent in 1926, it must have taken some time for Morehead to get production of his invention started and it appears that he had to look to overseas production to bring this to market. It wasn’t until the late 1940s/50s that the Chadwick Miller company began importing this Japanese made implement. The Roller Rule is very well manufactured and presented. There are no rough edges, both pencil propelling and measuring mechanisms work smoothly, ‘pull-apart’ elements are snug and there is no floppiness to be found anywhere. The entire measure shouts good quality and it looks very stylish, if of its time.

Pocket clip- 'USA PAT'D ROLLER RULE'
Pocket clip- ‘USA PAT’D ROLLER RULE’

a mechanical pencil with a built in yardstick

A description of the pencil appeared in a 1950 issue of Popular Mechanics. This report on the ‘yardstick’ simply states its usefulness for measuring any distance, with no mention as a map measurer. However it is only too apparent that many owners were using the pencil for that purpose, particularly as the one inch scale lent itself well to many road maps.

One complete rotation of the wheeled end-cap, or ‘Inch-ometer‘, measures two inches. This roller wheel end-cap has a rubber tyre fitted to stop it slipping on maps and other surfaces. Spare tyres could be purchased, costing ten cents for two.

The circumference of the cap has indications of fractions of an inch- 0, 1/4, 1/2, 3/4, 1, 1 1/4, 1 1/2, 1 3/4. There are also one eighth of an inch increments marked so it is perfectly possible to measure any scale distance up to 36 inches in one eighth of an inch graduations. And then, having reached 36 inches, simply continue measuring in the reverse direction. Perhaps unsurprisingly, I find it measures perfectly.

A short desciption of the Roller Rule was made in Popular Mechanics magazine. p155, March 1950
A short desciption of the Roller Rule was made in Popular Mechanics magazine. p155, March 1950
Roller Rule instructions, side 1
Roller Rule instructions- side one gives clear directions on usage.
Roller Rule instructions, side 2
Roller Rule instructions- side two includes examples on how to use the Roller Rule for mathmatical problems.

A contemporary newspaper advertisment informs us that each pencil cost $2.25. When purchased it comes with printed instructions, in a small card box with clear plastic slip lid on which the name proudly appears in gold paint

Roller Rule


The advertisement for the Roller Rule doesn’t hold back on rather expansive claims- ‘measures any surface‘, beside a cactus plant, ‘measures any shape‘, beside a camel, and finally, ‘measures any distance‘, beside the shape of the USA.

Advertisements for the Roller Rule promote its capability as a calculating instrument for mathmatical problems, however most contemporary accounts relate to it being used for measuring distances on maps.

Contemporary newspaper advertisement
Contemporary newspaper advertisement
Roller Rule and packaging in which sold
Roller Rule and packaging in which sold
Decently sized eraser is concealed within the pencil's body
Decent sized eraser is concealed within the pencil’s body
Short spare 'eads' of graphite, can be stored in side the pencil
Short spare ‘leads’, or graphite, can be stored inside the pencil next to the propelling mechanism

The measures is 150mm long with a 12mm thick barrel. It weighs 27g and is comfortable in the hand, not too thin or thick and easy to grasp. The short ‘leads’ are 1.2mm in diameter and spare graphite can be stored within the propelling end of the pencil.

The Roller Rule is a lovely relic of its time and still works faultlessly, whether as a measurer, or simply as a pencil.

The Roller Rule, one of the handiest measurers ever made
The Roller Rule, one of the handiest measurers ever made

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

3 replies »

  1. Fascinating, and as I read the article I had a vague feeling that I once possessed one as a boy (now 76 years old!)

    If so, I only wish I had kept it!!!

    Could you advise me of a good value wheel map measurer for my 2-8 mile walks, please?



    • If only we could have selectively kept so many items from our youth….
      I am reluctant to recommend any measure for purchase of todays market. Suffice to say almost any of the cheaply made analogue dial measure, which are all pretty much generic these days, will work just fine.
      Or, for the same amount of money you can buy a quality French or Swiss made measure off eBay, a hundred years old, that will invariably still work great. The only issue with an older measure is that they may measure in miles or verst (1 verst = 1.0668 km) so you will probably have to measure off your route by either back-rolling against the km grid that overlays a map, or along the scale line found at the bottom of an Ordnance Survey map


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