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The Kimberley diamond mine, one of the richest in the world, was discovered in 1871, setting off a rush by hopeful miners. In The South African Diamond Fields, and a Journey to the Mines the author describes the process of claiming plots of land by individual miners:

The Diggers' Committee, an influential elective body, had made it a rule that when such a rush occurred, each individual might mark out for himself with stakes a "claim" of 31 feet square...

(Note that this is 31 feet square, not 31 square feet.)

That looks like an odd number, both literally and figuratively. How was it decided? Did this Diggers' Committee (where did they come from?) give any reason for it, or was it derived from some older tradition?

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    I still have no idea where this originated so far, but apparently gold claims were the same size in Australia: historylfr.wordpress.com/gold-panner – Brian Z Aug 26 at 19:22
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    I visited the old mine at Kimberley as a kid. They said the claims were 30 Dutch feet square, which equated to 31 English feet.. I'll try to find a source later and post an answer if I can. – sempaiscuba Aug 26 at 20:20
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    This book says the same about Dutch feet, footnote cites another book from 1872 but I don't see it there. – Brian Z Aug 26 at 20:25
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    @Panzercrisis 31 feet square = 961 square feet ( 31 x 31). But a lot of the contemporary sources (wrongly) used the terms "feet square" and "square feet" interchangeably. It frequently creates confusion. – sempaiscuba Aug 27 at 23:15
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    @Panzercrisis Paynton, for example, often confuses the two. He says on more than one occasion that a claim was "thirty square feet". If that had actually been true, each claim would only be about five-and-a-half feet on each side. We know from the written sources that the claims were thirty feet on each side (Paynton also says "They say they can sift out thirty cartloads of stuff in a day, and work a claim of thirty square feet in three weeks or a month to the uniform depth of 18ft", so it is clear he means 30 ft square, and not 30 sq feet). – sempaiscuba Aug 27 at 23:26
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I visited the historic diamond mine at Kimberley as a boy. We were told that the claims at Kimberley were 30 Dutch feet square, which equated to 31 English feet. It seems the standard size for diamond claims in South Africa was 30 feet square.

In fact, it seems that was not quite correct. The Kimberley and de Beers claims actually used the Cape Foot, which was:

defined as 1.0330 English feet (and equal to 12.396 English inches, or 0.31485557516 meters)

So, 30 Cape feet = 30.99, or to a close approximation, 31 English feet.

Interestingly, the Wikipedia article notes that the Cape foot continued in use until 1977 when South Africa adopted the metric system. That kind of thing can happen when multiple standards exist side-by-side.


As Theodore Reunert observed in his Diamonds and Gold in South Africa, published in the 1890s, claims at Bultfontein and Dutoitspan used the English foot as the standard [p42].

It is worth noting that these mines were discovered slightly later than the Kimberley and de Beers mines (the first years of production in these mines were 1870 at Bultfontein, and 1871 at Dutoitspan), so they were less developed when the diamond mines were annexed under the proclamations issued by Sir Henry Barkly in October 1871. This might therefore account for the use of the English foot in setting out claims, rather than the Cape foot used previously.

The annexation of the diamond fields is described in some detail in chapter 9 of Sir Charles Paynton's The diamond diggings of South Africa. A personal and practical account [pp51-56], which was published in 1872.

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    Interest only: Making a Dutch square foot ALMOST exactly 0.1 square metre. Actually 0.099135 m^2 – Russell McMahon Aug 27 at 9:09
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    As if non-metric units weren't bad enough already, this isn't the only alternate definition of the foot. But at least one of them is going away: the US Survey Foot is deprecated as of 2022: thestreetjournal.org/2020/08/… (fairly interesting pop-sci article with some quotes from a metrologist.) – Peter Cordes Aug 27 at 9:35
  • @PeterCordes Is that article some a-b-testing deployment gone wrong? Every paragraph is repeated several times, with slightly changed wording. – SE - stop firing the good guys Aug 27 at 10:35
  • @SE-stopfiringthegoodguys: When I load it (with umatrix blocking some JS), not every paragraph is repeated. I think some "repeats" are actually photo captions or should be larger-font highlights, and are just one sentence from a later paragraph. I think that's the same article I read a few days ago on my phone, but I had to re-find it with google just now. Searching again on an exact phrase in that, it also showed up on dailymail.co.uk/sciencetech/article-8648459/… – Peter Cordes Aug 27 at 10:40
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    @petercordes It gets even worse: There were actual wars fought over border disputes because the treaty establishing said borders wasn't specific enough about which particular 'foot' was used as the metric. For all that it's fun to mock standardization, standards matter. – Shadur Aug 28 at 7:02

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