Antique Crosby Steam Gauge & Valve Co London Planimeter C1910

For sale are this attractive late 19th or early 20th century precision instrument retailed by the Crosby Steam Gauge and Valve Company of London. The instrument was originally made in Switzerland and appears to be some kind of planimeter, but I don't know its exact use. It comes with its original purple felt lined leather covered case which is about 22 centimetres in length and 3.5 centimetres tall. Total weight is 259 grams. Condition to both instrument and box is good with minor scuffing and wear only. Shipping will be free within the UK.