Working principle and Introduction: 891 Timer is manufactured according to the German standard size with compact structure and elastic clip mounting. Driven by synchronous motor, it has various voltage and frequency specifications to fit different usage requirements with 7-digit display. Its min. counting unit is 0.01 hour (36 seconds). Its continuous counting can last for 11 years. It will count time from zero again after full timing is completed, and it has no reset mechanism, so the counted time can not be lost.