Medieval "calculation string"

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William Prott
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Medieval "calculation string"

Postby William Prott » Fri Aug 21, 2009 6:10 pm

Good evening all,

A few years ago I saw a documentary on TV about an archeologic experiment, a replica of a medieval house was built using nothing but medieval construction materials, tools and craftsmanship. One of the things that struck me was a kind of "calculation string" used by either the bricklayer or the carpenter (maybe even both). It was a piece of string, 2 or 3 feet long with knots in it at defined distances of each other. By folding the string, or wrapping it around one's hand it could be used for various basic calculations, deviding but also fractions.

I have been on the lookout for an "operating manual" , or any more information i can get about such a string but so far all I got are raised eyebrows. Since I do not know a name for such a cord, googling gives me no firm clues either.

Is there anyone here who can give me some more information, please?


William Prott, captain of the Fortress Bourtange won the "battle near Jipsinghuizen" on 26th september 1666, killing 200 troops of the Bisshop of Münster

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Brother Ranulf
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Postby Brother Ranulf » Fri Aug 21, 2009 6:47 pm

I have not come across mention of a "calculation string" in my research into the 12th century; Alexander Neckham (who truly delighted in such things) only mentions a "calculating board" - a kind of table marked with a main line crossed by regularly spaced lesser lines and using metal or bone counters. This was apparently used in complex astronomical and trigonometrical calculations, but presumably could have been used for other applications.

A string marked with knots would simply be a more mobile version of the calculation table, so I don't see why it should not have been employed at some stage.

I have seen a 12th century illustration of masons at work, but the only string visible is a plumb-line to check the verticals. There were no bricks at this period, so we are talking stone walls.


Brother Ranulf

"Patres nostri et nos hanc insulam in brevi edomuimus in brevi nostris subdidimus legibus, nostris obsequiis mancipavimus" - Walter Espec 1138

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Lady Willows Retinue
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Postby Lady Willows Retinue » Fri Aug 21, 2009 6:51 pm

Basic Pythagoras right angle triangle - remember back in your school days - sides of 3,4,5 (inches, feet, cm metres, or whatever). Same system as supposedly used by the Egyptians.
Knots on your rope should be at equal distances to divide the rope into the ratio 3:4:5 - total of 12 sections.
Join the 2 ends. Peg out 3 sections in a straight line, then form a triangle with the other corner at 4 & 5 lengths - gives a right angle.



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Brother Ranulf
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Postby Brother Ranulf » Fri Aug 21, 2009 6:58 pm

Looking back through my notes I have a portrayal of a Master Mason discussing a building project with Henry II - the mason is holding an L-square and a pair of compasses (something like a sergeant-major's pace stick). No strings, I'm afraid.


Brother Ranulf



"Patres nostri et nos hanc insulam in brevi edomuimus in brevi nostris subdidimus legibus, nostris obsequiis mancipavimus" - Walter Espec 1138

William Prott
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Postby William Prott » Fri Aug 21, 2009 7:22 pm

The string was just as it sounds: a string with knots, just imagine a 1 foot string with a knot every inch. If you devide a foot by four, simply fold the string twice so there are four equal length pieces. Count the pieces in between the knots and you will find the answer: 3 inches in a quarter foot.

But there was something more to the string, the knots were not equally spaced so a bit more complicated calculations could be made. It is just that "more complex" part that intrigues me. The Pythagoras (common ratios) thing Lady Willows Retinue sais may have something to do with it but there was no mention of joining ends or making triangles or other shapes .


William Prott, captain of the Fortress Bourtange won the "battle near Jipsinghuizen" on 26th september 1666, killing 200 troops of the Bisshop of Münster

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Laffin Jon Terris
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Postby Laffin Jon Terris » Fri Aug 21, 2009 7:28 pm

Jack the Dodgy Builder was explaining this to me at Kentwell this year, he is the man to ask.

JonT


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William Prott
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Postby William Prott » Fri Aug 21, 2009 7:33 pm

Ah thanks a lot! Is he a member here? I couldn't find him in search mode.

Sorry, found him. Will send him a PM, thanks again!


William Prott, captain of the Fortress Bourtange won the "battle near Jipsinghuizen" on 26th september 1666, killing 200 troops of the Bisshop of Münster

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Lady Willows Retinue
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Postby Lady Willows Retinue » Fri Aug 21, 2009 7:37 pm

The ratios bit is still used today. When marking out an archaeological trench, we usually get our right angles by using the measuring tapes to get the 3:4:5 lengths.



William Prott
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Postby William Prott » Fri Aug 21, 2009 7:44 pm

thanx. That's quite smart and may very well be useful to me when I will start building my dogs kennels . :)


William Prott, captain of the Fortress Bourtange won the "battle near Jipsinghuizen" on 26th september 1666, killing 200 troops of the Bisshop of Münster


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