Unidentified Rule

Good morning.

This rule, which appears to be made of either bone or ivory, was amongst my gandfather's tools who was an engineer, designing tools. I have absolutely no idea what it is for or whether it is even a measuring rule at all.

I should welcome any information on it.

James.

Edited By James Alford on 25/02/2018 11:10:48

I'll dive an and say ... I haven't gota clue.

One interesting thing is that the angle scales measure out from the centre.

The straight scale appears to be ordinary inches from the end.

Could it be a scale rule?

Brian

Hi, it is an Ivory sector rule, very nice item, is there a makers name?

Martin

Edited By James Alford on 25/02/2018 20:09:21

“What is a sector rule”

There is a fairly comprehensive explanation on Wiki

Hello James.

There are currently seven sector rules on ebay at a variety of prices, all fairly high, all similar to yours.

Wikipedia has a long explanation detailing the various scales on the rule. Further editing seems to be needed on most of the scales. The origin of the rule appears to have been Italy in the early seventeenth century. It allowed the user to perform a number of calculations, some stated, and others described as 'complex'.

Put 'sector scale' into google or whatever, and be prepared spend some time looking at the various items that come up, because it does not take long to become complicated and complex.

Regards. Mike.

Good English makers increase the value of these and they can be highly collectable. Does it have tiny brass 'buttons' with a dimple in the middle for divider points to avoid wear?

Martin

James - Sine, Co-sine and Tangent ,Log ,T* - Tanh, S* - Sinh, C* - Cosh. I don't remember how they worked, but seem to remember something at college 50 odd years ago when we made our own on white card strips.

Ah - the web to the rescue
BobH >**LINK**

Hi James, Looking at the middle 2 pics it appears to me that possibly it is bone not ivory, particularly as there is no makers name. Does close inspection show microscopic porosity in the stained brown areas near the hinge joint?

Also the slight warping in the middle is more common to bone.

There are varying quality types of these, some also made in boxwood.

Cheers, Martin

hi,

French & English sector (the ancestor of computer)

pm

Fascinating, I want one.

Slide rule forerunner perhaps?

Damn clever our forebears weren't they?

Martin:

I have had a look at the material with a magnifying glass. Rather than porosity, the structure seems to be more like very fine lines, like the grain in some cuts of beech wood.

BobH: thank you for the information about sines et all and the link to the web page. I have had a look at it and it has shed a lot of light on the tool. All I can say is thank goodness for modern calculators.

Regards,

James.