4-figure Vernier Romer

Some time ago, I wanted to plot the positions of archaeological features on the Dorset & Purbeck 1:25k map (yes, I was that bored). It got rather tedious with a ruler, so I came up with the idea of a Vernier Romer. This allows you to read 4-figure references from the map with relative ease, using the long-established principle of vernier measurement. The two elements of the vernier are formed by the romer grid and the map grid; where they intersect is the vernier measurement.

The Vernier Romer can be seen in the first picture (you’ll have to excuse the poor image quality; low resolution JPEGs don’t do justice to this sort of thing). It’s like a conventional romer, only a bit squiff.

To take a reading, you place the Romer on the map, and put the little red cross on the feature in question (in this case, a church), and then make sure the romer is horizontal, using the map grid lines and Romer outline for guidance.

You read the first two figures from the map as usual, and then take the third as you would for a normal romer. For the fourth figure, you follow the grid line until it cuts one of the romer diagonals; then read across to find the fourth figure. 3-figure Eastings are read off the top edge, 4-figure eastings off the left-hand edge, 3-figure Northings off the right-hand edge, and 4-figure northings off the bottom edge.

An example is shown in the second picture. The two-figure reference from the map is 02 01. Now read the Eastings value by following the green line; starting along the top edge, the third figure is 1, and follow the grid line down until it meets the vertical vernier line. Now follow this across to the left, giving the fourth figure as 7. Read the Northings value by following the purple line; starting along the right edge, the third figure is 4, and follow the grid line across until it meets a horizontal vernier line. Now follow this down to the bottom, giving the fourth figure as 3.

Combining the parts of the reference, we see that the full 4-figure grid reference is 0217 0143.

(By the way, just to be clear, the green and purple lines are solely for the purposes of demonstration; they don’t form any part of the Romer. Or the map…)

The basic Vernier Romer can be incorporated into other navigation aids, such as a Portland plotter, to make a useful complement to a map and compass.

The original romer images are created in PostScript, and can be printed on laser printer transparencies. Simple scaling factors in the PostScript code allow for printer scaling errors to be corrected. The PostScript code can be found in the tenth post on this thread.

Images

sketch 1
Image I

sketch 2
Image II

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Notes

Profile Kevin Beeden

paranoia products are a team of dedicated, but imaginary individuals, specialists in every aspect of outdoor enterprise.

(In other words, it’s all in my head)

Entry submitted on 30 Nov, 2007

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