This has me stumped.
does anyone have a clue as to where and by whom this would have been used?

due to the fact they are not printed on "economy" paper and the aircraft included i would guess printed around 1940/41?

the publsher is BTH (British Thomson-Houston) an large engineering firm who were based not far from me in warwickshire.
during the war i believe they produced aircraft magnetos amongst other things.

I cant find anything like these books online.

Also what is a "50mph relative speed ring"???

any ideas greatly welcome!!!

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