A pocket air meter by Negretti and Zambia of London. In the original leather case and with the original steel and brass adjuster too. I’ve always loved these wonderful little pieces of engineering and the way they pick up the lightest of breath. 
As a nice little extra there’s also a calling card in the box from a W.H.Hunt of 12, New Oxford Street, telephone Holborn 3827!
Leather box : 9 x 10 x 5 cm
Air Meter : 8 cm in diameter