Another little gadget, this time a map measurer

Another measuring instrument. It’s not quite as original as the previous one, and it was made in a specialized factory, but I liked it all the same.

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This post is about a map measurer, whose name comes from two words: Curve and Meter. Interestingly, in Russian it isn’t called a curve measurer or a curve-measuring device :) — it’s called a curvimeter.
Anyway, I’ve wandered off topic.

It comes in a compact cardboard box, and the only thing included with the instrument is the manual.


The manual has yellowed with age. I tried to make out the publication date, but couldn’t, so I’d guess it’s from the early 1980s.


It looks quite compact and even has the quality mark.


The instrument is extremely simple and displays the measured length in just two units: centimeters and inches. The scale division is 1 mm in the first case.
I found some fibers under the glass inside, which slightly impede the needle on its return. There’s no reset button, so you have to set it to zero manually, though that’s not particularly difficult.


I mentioned its simplicity for a reason: most instruments of this kind have several measurement scales on a single dial. This one has two scales, each with just one unit, although adding another would not have been technically difficult.
Interestingly, the Ukrainian version of the Wikipedia article about curvimeters shows exactly the same model as the one in this review :)


Curvimeters were often made at watch factories, and the operating principle is extremely simple. There’s a small wheel at the bottom; roll it along a curve (for example, a road on a map), and a gear train transfers its rotation to the pointer.
The only catch is that the mechanism has to run very smoothly, and the wheel needs good traction on the surface, so it was made ribbed.


I found the price on the instrument’s case. I think anyone who lived in the USSR will recognize this kind of price tag. This one cost 2 rubles, or 10 servings of plombir ice cream :)


I didn’t take it apart, but I did try taking some measurements. Here I measured a straight line, and was a little surprised to see that the instrument read slightly low. The photo shows the best result; the difference reached 2 mm.


A friend and I decided to investigate this quirk.
We took a sheet of paper, a more accurate (presumably) ruler, and rolled the instrument along it again. Everything was fine: over a 270 mm stretch, it read exactly 27 cm.


We used the same ruler, but this time rolled the instrument over the tablecloth instead of the paper. The result was low again.


I suspected the fabric’s texture was to blame, since it clearly interferes with the instrument’s measuring mechanism.
We repeated the experiment and got the same result: on paper, the difference was within the measurement error, but on fabric, the reading was low.

My guess is that the fabric stretches as you roll the instrument over it, so by the time you reach the endpoint, it has stretched and the instrument has traveled a shorter distance. In other words, the fabric is 270 mm long in its normal state, but if you stretch it slightly while measuring, then once it returns to its original state, that section will probably be a couple of millimeters shorter.


This little instrument is simple but interesting in its own way. Of course, it can’t compete with modern technology like Google Maps, but it does have one important advantage: it works without an internet connection :)

That’s all for now. Take care!