Brass curved clinometer by G Davenport & Co of London EC

I was recently given a brass curved spirit level which I think is an early aviation (or automobile) clinometer which belonged to a chief member of staff at the Alvis company in Coventry and I’m intrigued to find out its history.

It is 7 inches in length, with a fixing hole of approx 5/32″ at either end and is approx 5/8″ wide x 1/2″ deep . It has a bubble glass running the full length and inscribed in the brass on the left side above the bubble glass next to the fixing hole is “ascend” with graduations from 7 10 15 up to the middle of the curve then the same graduations to the other side of the curve reversed 15 10 7 down to the word “descend”. Below the bubble glass from the left side the graduations read 3 4 5 6 8 12 and 20 up to the middle line then reverse 20 12 8 6 5 4 3. At each fixing hole is inscribed 1 IN – I don’t know if this is for say “1 in 10″ or 1”
It is stamped G Davenport & Co Ld (sic) London EC on one side of the frame and Registered No. 601578 on the other.
I’ve tried to attach a photograph but don’t think it has worked. Hope someone can give me some further info on this, the guy who gave it to me, a sprightly 88 year old, worked at the Alvis for many years and ended up in a senior position in Quality control. We had a good chat about the Leonides a/c engine the last time we spoke.