ID: 
1550
Maker's Name: 
E. R. Watts and Son Ltd.
Where made: 
England
1927
Dimensions: 
11.3 × 4.2 × 8.2 cm

Contains a small telescope and a bubble level that can be seen simultaneously with a distant target.

When the target lines up with the bubble, the angle of elevation can be read off the adjuster scale.