It might be a vintage electronic pacing or tracking accessory from the 70s, likely designed for use with a stationary bike, treadmill, or possibly even a vehicle. The branding “PM” and the labeled buttons like “MILES,” “SPEED,” “TRIP,” “SLOW,” “FAST,” and “CLEAR”, suggest it was used to monitor or simulate distance and speed, possibly for training or exercise purposes. P stood for Pacer, and M was either Module or Monitor.

On the rear of the box there might be another label that is marked PM100 or maybe PM1