A finely made example of the early Mark I version of the iconic Balloon Pilots Slide Rule, made by James J Hicks of Hatton Garden London. 

This rule is marked with the number 589/31 - which I believe means this dates from 1931 - making it quite an early version. W F Stanley took over the firm of J J Hicks in 1911, so it's likely all of these Hicks branded Mark I's were effectively Stanley-made rules.

This being the Mark I, we have 3 brass framed glass cursors and a double/split central slide.

Comes in the original leather-effect case with blue silk and velvet lining. Great condition - just a small crack in the glass of one cursor.

Case measures 64.5cm x 8cm x 3cm.