Halden Calculex complete set pocket watch slide rule 1950 England

This small round slide rule is from the United Kingdom and made by Joseph Holden. It is the later patented version of the Calculex and comes complete with the booklet and leather pouch. I am guesstimating this one is from somewhere in the 1950’s and has the pocket watch style shape. It is fully functional and easy to operate. The condition is very crisp and near mint with the very white dials and no discoloration to the plastic glasses (they tend to turn yellow when often exposed to sunlight). The construction is also not waterproof zo it can let in dirt and moist which take their toll. It measures ca 6 cm or 2 1/4 inches in diameter. Check the video on how to work your vintage man tool : slide rule operation instructions!