Elephant can function as a large general purpose computing device. Despite its technological advances, it is often criticized more than the average computing device. By 1936 Knemeyer's invention of the "Dreieckrechner" hand-held flight computing device, similar to American Lt. No irreversible computing device can use less energy than this, even in principle. It is a wearable computing device running a modified version of the Android operating system. A Turing machine is a hypothetical computing device, first conceived by Alan Turing in 1936.