1. Many slide rules are hard to place - but this is more difficult than most.
2. The material of the rule the has the appearance of yellowed bone - under a magnifying glass its texture is more akin to bone than plastic. The groves for the slide and the cursor appear to have been machined not moulded.
3. Marc was a trade mark of Unis - but most Unis rules have their own logo. Was this made before or after the logo was introduced? My guess would be before.
4. When I received the rule, the cursor was covered with sticky, black gunge. When I cleaned that off the cursor appeared to have been made of aluminium but brass coated!
5. The rule has an inches scale on the front and a centimetre scale on the back. I bought this rule via the US so it may have been made for export  - hence the wording in English "Made in France".