An auto shut-off function switches the unit off after 5 minutes. Durable ergonomically-designed, durable black case with rubber bumper strip increases ease of use and durability. Hold tach 4-6 inches away from propeller for use. This Tachometer uses a sensitive photocell to measure the number of times the propeller blade crosses between the sensor and the light from the sun. In the event the readings become erratic, change the direction of the model is facing by 90 degrees and take another reading.
Instructions are on the box.
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