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noel shelley12/03/2021 11:02:34
1436 forum posts
23 photos

What is it, and what is it for ? Copyright date is 1908. Some sort of circular slide rule or calculator ? Noel97934.jpg

Oldiron12/03/2021 11:20:50
995 forum posts
40 photos

It appears to be a calculator that can be used to add fractions together. Also seems to be in 1/64th increments. I have a huge collection of calculators & sliderules but this one has escaped me.

envious regards

Edited By Oldiron on 12/03/2021 11:21:05

Martin Connelly12/03/2021 11:26:14
2178 forum posts
227 photos

I think it is something to do with ounces, pounds weight and stones. The 16 times table in the corner is ounces in a pound. The numbers from 0 to 18 have fractions such as at 12 has ¾ which is the fraction of 16 that 12 is.

Martin C

Oldiron12/03/2021 11:31:28
995 forum posts
40 photos

Well spotted Martin. I missed that. I have sent a copy of the image to my FIL who is a Prof of Mathmatics maybe he has seen something like it.


Michael Gilligan12/03/2021 11:40:19
20289 forum posts
1064 photos

Most intriguing !

Copyright 1908 ... but no branding dont know



Edit: Probably drifting already ... but there may be some ‘leads’ amongst these:

Edited By Michael Gilligan on 12/03/2021 11:53:09

Nigel Graham 220/03/2021 00:19:39
2261 forum posts
33 photos

Are you sure one of these didn't inspire Philip Pullman?


I was tempted to think weights and measures, maybe Compound Arithmetic, as the printed sectors and outer dial suggest Base-20 arithmetic (20s = £1) - count 1 to 19, then 0 and carry 1.

Yet other aspects don't quite square with Avoirdupois or £sd; and anyway, that would not explain why some sectors have more than their fair share of odd "sums" and others have none. The inner dial has 30 numbered holes - there was a 30d coin (Half a Crown, = one-eighth of a £ but I doubt that was a common factor in such arithmetic. Though all those 12-denominator fractions might (mis-?) lead us into thinking shillings & pence.

It is hard to see any sort of ordinary shop-keeping pattern to it all, and it would take someone more numerate than I to analyse the fractions to pick out the pattern that probably does exist - and to establish why some sectors have none.

Lets look at the progressions in 1908:

Coins & values:

1/4d, 1/2d, 1d, (2d?) 3d, 6d. Then 1s (12d), 2s (24d), 2/6 (30d), 5s (60d),

10s note. £1 (=20s = 240d), £5, £10, 20, £50 notes

Weights Avoirdupois (does that mean, "have some peas" ? )

1 ton = 20cwt. 1cwt = 4qrs. 1qr = 2 stone. 1st = 14lbs. 1lb = 16oz.

The ounce was sometimes quartered but smaller weights still were usually in apothecaries' units like grains and drachms; and didn't the jewellers have their own scale based on the Troy Ounce?

Nothing really in that lot to correspond coherently and completely with everything on that.


Enlarging the screen, which has now stuck on very big and won't revert, shows what I'd thought was a bit of hanging-up string is actually a detent or pawl that appears to stop the central dial with its 30 numbered hollows, from being rotated clockwise when the outer dial is turned in that direction as instructed. The flattening by its stop-pin might allow it to be raised for quickly setting the dial backwards to any particular number.

What do all those little holes round the edges do? They are too numerous for merely holding the device to a surface, and all lie on the radial lines. Or the extraneous holes in the outer movable dial.

Is that loop of wire held by the screw, a simple friction-spring, or part of a broken pointer?


Whilst Martin could be right about lbs and oz (fractions of 16), I am not sure that applies to all the fractions suggested - well, not without testing them all. There are a few that would correspond, such as 7/8lb (14oz); but I don't think traders and other users ever tried thirds and fifths of pounds.....

Ah! Sudden thought. Binary values (8, 16, etc). 1/3rds, 5ths.... Musical? I wonder if it had something to do with organ-building and tuning? Organ voices are referred to their ranks' fundamental pipes, which are expressed by tone name and pipe length in feet and fractions thereof; and of course, doubling the length halves the pitch. I could be well wide of the mark, but if this device is a wind-instrument calculator it might account for some of the curious values shown, and the gaps.


Try doing some sums with it, referred to the above, and see what you get! (I think I can still remember the basics of Compound Arithmetic, taught in Primary Schools in my day when Arithmetic was not a dirty word and Mathematics was done in Big School.)

And you thought the Antikythera Mechanism baffling?

SillyOldDuffer20/03/2021 09:54:47
8863 forum posts
1995 photos

Following on from Nigel's analysis, I notice:

  • The arrows show the wheel turns clockwise only, suggesting additions.
  • The radial lines and pin holes suggest angles.
  • The pin holes suggest pricking through on to paper as was done on nautical charts to avoid defacing them with pencil or ink. I don't think it's navigational, possibly a layout tool.
  • There are 20 main sectors and the inner circle has 30 locking points, a 2:3 ratio, not a vernier. (We don't know what the actual ratio is.)
  • The full circle is graduated 0 to 288 (Assuming the sector numbers match the bottom right 0 to 9 table ascending in 16s ).
  • Sectors 0, 7, 11, 15, 16,17, 18 and 19 are blank. 15 to 19 being blank suggest only 3/4 of the scale is relevant. Might be significant that 0, 7 and 11 are prime numbers.
  • The fractions don't seem to make any sense! ½ ⁴⁄₈ ³⁄₆ ⁶⁄₁₂ are obvious equivalents, but not why they are in sector 8. Plenty of other inconsistencies: sector 3 is marked ⅕ + 1, while sector 9 has ⁷⁄₁₂+1 and the much bigger number ⅗+9.
  • The largest divisor is 12, in the set 2,5,6,8,9 and 12.
  • The turning discs also look to be pin-holed, again suggesting angles.
  • Copyright 1908 suggests a commercial ready-reckoner rather than a navigational, military or mathematical aide.

I've no idea what it is!


Michael Gilligan20/03/2021 10:45:52
20289 forum posts
1064 photos


This is probably unrelated ... but it might set us thinking in a field other than weights:


[ this one is for optimising the use of wallpaper ]


ega20/03/2021 11:06:15
2565 forum posts
203 photos

Is there any information on the reverse of the device?

noel shelley20/03/2021 11:13:05
1436 forum posts
23 photos

Gentlemen, Thank you so much for the effort being expended. The question came from an engineering friend. We have no more information than the picture, I will see wether any more can be found. Once again Thanks. Noel

Rob McSweeney21/03/2021 13:03:12
73 forum posts

Could it be possible we are not seeing the complete device? Might this be the 'setting' element?

Nicholas Farr21/03/2021 13:25:20
3415 forum posts
1590 photos

Hi, I've been thinking along the same lines as Rob, maybe there should be one or more pointers or something that peg into those little holes on the two rings and they may point to the little holes on those lines on the square bit, which have alternating one and two holes and then maybe, it would be used to set a machine up for a particular sequence in a production run. As it is, to me the set out of all the numbers etc. don't make much sense. Of course I am probably completely wrong.

Regards Nick.

noel shelley21/03/2021 13:56:26
1436 forum posts
23 photos

Having contacted my friend, one thought that has come from else where is that it might be connected to surveying or architecture - does this shed any light on the matter. It seems in very good condition. The reflections in the picture indicate that A) it is of thin material, aluminium or tinplate? B) it is pinned in place by the four corners? and C) it was not a costly device? Just some thoughts ! Noel.

Rob McSweeney21/03/2021 14:39:45
73 forum posts
Posted by noel shelley on 21/03/2021 13:56:26:

Having contacted my friend, one thought that has come from else where is that it might be connected to surveying or architecture - does this shed any light on the matter. It seems in very good condition. The reflections in the picture indicate that A) it is of thin material, aluminium or tinplate? B) it is pinned in place by the four corners? and C) it was not a costly device? Just some thoughts ! Noel.

If it is aluminium, we should bear in mind that back in 1908 when this device was made, aluminium was regarded as 'the new wonder metal' and was being used for jewellery and the like, so not necessarily inexpensive.

MichaelR21/03/2021 15:01:29
478 forum posts
78 photos

Just to confuse matters, I think it could be a very early Light Exposure calculator for cameras of the day.

Just a wild guess.


John Haine21/03/2021 15:11:56
4712 forum posts
273 photos

It's a post-kythera mechanism...

Howard Lewis21/03/2021 15:41:49
6301 forum posts
15 photos

If for photograhic exposure, in 1908 the stops would probably have been the old Uniform System, rather than the F No. system, so the values would have doubled. At that time, probably no one imagined a capability to make a lens with an aperture larger than what we now consider to be f/8

US4 equalled f/8, US 8 = f/11, US 16 = f/16, US32 = f/22, US 64 = f/32 and US 128 = f/45

Thus as each number doubled, the area became half that of the preceding number.

Since prime numbers are present, photography seems unlikely a use.

The fractions in the sectors with the integers are intriguing. 7/8 being 14/16 I can follow, but the 11/12+2 foxes me.

5/6+1 would be 11/12, not 13.

So doesn't look like £ s d, , feet and inches, or Avoirdupois weights, so totally baffled. Not sure about rods, poles, and perches! Some form of area calculator.

Maybe there would be an instruction saying something to the effect of "Place sector 9 against...., and read the result in...."

IF only there was a n instruction book with it, all would be revealed..

Reminds me of being asked to find out about what looked like two 5" slide rules one above another in a common body. It was marked "Cock" "Maker". The only suggestion was that anyone using it would make a cock of the job!

Sorry to have included nothing of any further value.



Edited By Howard Lewis on 21/03/2021 15:42:16

Nigel Graham 223/03/2021 22:48:57
2261 forum posts
33 photos

I can't see it being a ready-reckoner for general use, but something dedicated to a particular trade, especially as it has such an apparently-random assortment of numbers and fractions, with some numbers lacking fractions..

Noel Shelly offers architecture or surveying - I suppose it might refer to commercially-standard materials of its time.

Michael R wondered about photography.

I pondered musical instrument, especially organ- building.

Dave (SOD) has given us further analysis of the scales.

Nicholas Farr suggests it was for setting some particular production-machinery.

Based on that, here's a bit of completely marking-blue-skies thinking as I do not actually know... Textiles weaving / knitting by machine? For example, lace: my Grandad had been a "lace designer", meaning he did not design the ornate fabric itself, but the cam-drives that produced it on automatic looms, in the Nottingham lace industry.


I wonder if anyone at the Science Museum would know?


The shiny finish is not bare metal - not tin-plate and certainly not aluminium. Enlarging the image shows it is a pale cream colour, so probably painted or enamelled, and perhaps screen-printed. If used as Nicholas suggests, it was probably screwed to the machine or to an adjacent wall; and its excellent condition suggests clean working conditions (partly leading my fabric-trade thinking). .

Whatever this was for, it's certainly giving us some fun trying to find out!

Michael Gilligan23/03/2021 23:24:35
20289 forum posts
1064 photos

I’ve just found a somewhat clearer image of it [or the other one!] here:


... still none-the-wiser though sad


Chuck Taper24/03/2021 08:14:51
41 forum posts
4 photos

If you have the physical device........

Would it be possible to re post the photograph showing the device next to a rule.

Alternatively post some dimensions.

If not above possible would anyone hazard a guess at sizing based on limited information.


Frank C.

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