Product information:
Color classification: Black
Size: 90x54x16

Features: 

Tachometer can be used for two-leaf paddle to nine-knot paddle paddle blade speed test, and the measured speed range is 0-99999 rpm.
The tachometer contains a 3V 220mAh button lithium battery. LED display screen makes reading more convenient.
Turn on the POWER button for a long time, and then press the set button above 1 "to turn on the backlight!
Press set to select the number of blades of the test propeller!