NavList:

Trying to get an answer from Weems & Plath, but taking forever as their reply said had a high volume of inquiries and responses would be delayed.

 Found a very nice old handheld pelorus with magnifier and light in a wooden box with its own window on a side door and rotary light switch on the box itself. You don't have to remove from the box to use it if lit.  It was in a marine consignment shop.

 So far it appears in excellent order except the air bubble is a bit oversize.  This appears to be identical to one sold by Weems and Plath in the past, and originates from Japan. It appears W & P branded the Japan model at some point under their logo.  Hence my question to them. No date yet in my research. Going to sit down with it and try to figure out more on boat this weekend. Maybe 60's to 80 ish as a guess? 

I am trying to verify what fluid to use.  I believe current W & P fluid is Isopar M.  Ritchie also sells pints of fluid I think are Isopar L.

I recall various versions of older compasses using mineral oil, purified kerosene, or alchohol mixed with distilled water depending on use and maker.

Would any of you happen to know about compatibility for this older unit?  I'm not sure what might safely mix or cause harm.

I had experience topping off compasses in my younger days aboard various craft before it seems sealing got to be more perfect.  Also compasses were less throwaway and more heirloom in design, so you would refill and service vs bop down to the chandlery & buy another. Compass fluid was more common and  the manual told you such esoteric secrets of the sacred scrolls routinely. 

I love this unit, as I use a pelorus and three arm protractor in triangulating diving positions in near shore work, doing celestial body bearings, and using that or my box compass as a quick verifier check on helm compasses when needed.  Most boaters and, sadly; boat manufacturers; are totally clueless about the magnetic compass and interference.

When I bought Syrena there was a big PA speaker with 4" magnet less than 3' in front of the compass. That speaker is now relocated up the radar mast.  On Petrel, which I ran 20 years; wiper motors were a foot away from the steering compass, and you could actively watch the card swing back and forth with the motor. The deviation  table looked like a disaster table.  I tore the boat apart and moved speakers, wiper systems, dash equipment etc. till I was within a degree or so all the way around pre compensation.

Anyway, I digress with my peeves at modern civilization.

Anybody have a guess what this might be filled with and safe topping fluid? I can get pics tomorrow if needed when I get back to sea.