An amazing £5 from LloydsPharmacy. I spotted the same machine in a shop for Euro70 in Finland!
It works by bio-electrical impedance by passing an electric signal through the body when holding the unit in both hands. Fat is more resistant than muscle and other tissues in the body, thereby allowing the Hand Held Body Composition Monitor to calculate the Body Fat %.
For my age range, at 28.1% I'm in the Body Fat High category (22-28%) borderline to Very high Body Fat associated with obesity 28%+. The healthy range is 11-22% body Fat. (BMI 25.7, 11st 10lbs)