Hartzell HC-E3YR-7 Owner's Manual page 215

C. Tachometer Calibration
(1) Hartzell Propeller Inc. recommends that propeller
owners/operators calibrate the engine tachometer in
accordance with the National Institute of Standards
and Technology (NIST) or similar national standard
(traceable).
(2) Contact Hartzell Propeller Inc. if it is determined that
a propeller was operated in a restricted RPM range
because of a tachometer error.
MAINTENANCE PRACTICES
Propeller Owner's Manual
136
61-00-36
Page 6-31
Rev. 2 Feb/17