Why is a 10-watt bulb called zero bulb?

Technically, it is not possible to light an electric bulb without drawing input greater than zero watts. Zero watts is actually not zero, but refers to the minimum wattage. The inaccurate electric meters of the early days could not measure such a negligible amount of consumption as during those days, the watt hour meter had a rotating disc and when all the other lights were switched off, the disc would have only minimum rotation, which would not record even a 10W consumption. This led to the origin of the term 'zero-watt', though it is incorrect. Nowadays, electric meters can record even electricity used as indicators in switches.