Any ideas on this plumb bob square

[merlin]

I have recently been given this lovely old tool by a good friend ,it is made out of Mahogany ( I think ) and brass with a lead tipped plumb bob that is locked away in its own little compartment when its all folded up.
It is a 3' x 3' right angled triangle that folds flat with a sprit level on one end and has a small belt to keep it together, it opens up to reveal a plumb bob and a brass peg that pushes into a brass hole, it locks together with a neat peg and cam lock - when it is held up there are different scales to coincide with the string line on one side and a protractor on the other side.
The makers name is PB&S ltd, there are also other increments on the edge that includes IMB1, IMB2 and IMB3 that line up when folded flat.
The angled scales might be to measure the pitch of a roof etc using fractions as a scale ?
Any thoughts....

Merlin

 

[MikeG.]

I've no idea about your tool, but I can tell you that roof pitches were traditionally in inches per foot. So "13 inches in 12", for instance, meant 13" rise for every horizontal foot along (47 ish degrees). I don't know if this helps understand the scale, or not.

 

[Orraloon]

Plum bobs and plum bob levels have been used since ancient times. The spirit level has replaced the pb level but some would argue the plum bob was more accurate.
http://www.plumbbobcollectors.info/42014.html
Regards
John

 

[merlin]

Thanks both of you - makes sense now as one side is just a big protractor and the other side is measuring pitch at inches per foot.

On the edge is inches and feet but still not sure what IMB is about.

As to who would use it I'm not sure as carpenters have used roofing squares for ages so maybe a surveyor .

Merlin

 

[John Brown]

No sensible help from me, but when I read "plumb bob square ", my brain adds "pants".

 

[AndyT]

This is only guesswork, but since we are collectively pretty good at recognising woodworking tools and their makers, I don't think it's for a carpenter, but for a different trade altogether.
Two possibilities would be boatbuilding (though I've not seen one like this in any YouTube boat building videos I've watched) or stonemasonry, where I can imagine it could be useful.

 

[merlin]

Andy I think you may have it with the stonemason as its main user, it would be useful for setting out buttress walls etc.

Merlin

 

[Orraloon]

Would explain why features in masonic images.
Regards
John

 

[toolsntat]

Not 100% but I don't think any I've seen including mine are devoid of the crows foot ministry mark.
In this instance I know exactly where mine is and I will have another look.
Cheers Andy