[Mystery all-brass slide rule. What was it used for?]

Hi there,

 

I have this weird little brass rule that has been gathering dust, as I don't know who made it, when - or the likely purpose. 

 

I wondered if anyone has seen one like this before, and what its original purpose might have been?

 

Not sure if it's clear from the photos, but this is quite small - just over 7 inches long, and 3/4 of an inch wide, with the brass cursor being 1 inch wide.

 

It carries 2 scales on the up side of the body (0 to 165 and 0 to 11.5), one scale on the central slide (0 to 14.5) and another full length scale on the reverse of the body (500 to 4200). It also has a graduated scale on the cursor itself (0 to 4 in quarter divisions). The numbers are so tiny, they are hard to see without a loupe.

 

I realise these things can be unfathomable without a user booklet, but any help you can give would be most appreciated.

 

Kind regards,

 

Russell