The LM series has been designed as a sealed, digital hour meter suitable for monitoring and recording elapsed running time. This is displayed on a digital LCD and normally shows hours and tenths of hours. They are ideally suited for applications where maintenance needs to be carried out on expensive manufacturing or transportation equipment after a desired time frame of operation.
For added protection these devices feature a 40-year memory data retention without power. They also have a long reset time to offer customers the protection against malfunction of reset.
These are usually under the STC of the aircraft. You must verify which one the aircraft parts list calls out and we always recommend confirming with your A&P before installing any part on a certified aircraft.