LEESON NEMA 1 PWM Control: M1740008.00 - Manual (Page 9)

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Minimum Speed (MIN)
The MIN trimpot (P502) sets the minimum speed. Turn the speed
adjust knob full CCW (but do not turn off) before calibrating the MIN
trimpot. Adjust the MIN trimpot until the motor rotates at the desired
minimum speed.
Calibration
Each drive is factory calibrated to its maximum horsepower rating.
Readjust the calibration trimpot setting to accomodate lower
horsepower motors.
All adjustments increase with clockwise (CW) rotation and decrease
with counterclockwise (CCW) rotation. Use a non-metallic
screwdriver for calibration. Each trimpot is identified on the printed
circuit board.
Maximum Speed (MAX)
The MAX trimpot (P501) sets the maximum speed. Turn the speed
adjust knob full CW before calibrating the MAX trimpot. Adjust the
MAX trimpot until the desired maximum motor speed is reached.