Item Idendification - Artillery?

[Diabolik]

Hi there

I purchased this recently and am trying to establish its exact use?!

I thought artillery related, to establish range and sighting adjustment, thus the graticals ?!

The leather case seems large enough for two of these fold out rules and there are 4 x stakes thus maybe one folding rule missing?

Any ideas from you knowledgeable crew out there would be gratefully appreciated.

Thank you