Romer (tool)

Made from transparent plastic, paper or other materials, reference cards are found on most baseplate compasses.

The scales are laid out in reverse, such that by lining up the numbers given in the grid reference with the gridlines for the square in question, the corner of the Romer lies on the location the grid reference of which is being read.

Some transparent versions have a small hole at the origin when this is not at the corner of the reference card.

While Romers of various designs are available commercially, they can easily be made by hand, by using a computer, or by finding a website[2] with instructions.

[3] A version was later developed for car navigational rallies by car rally partners Eric Gardner and John Cridford during the early 1950s, the 'Garford Romer' was available for both imperial and metric Ordnance Survey maps and is still sold today.

This illustration shows how the Romer is used. Here, we are plotting the reference 696018. The marks corresponding to (6, 8) on the Romer are lined up along the gridlines (69, 01). The hole near the corner yields the exact point, the church at Little Plumpton .