Plug your Firefly altimeter (not included) into the Firefly Field Data Display and the large built-in LCD will display apogee altitude, maximum speed, descent rate, battery voltage, and more.  Easily change between multiple SI and metric display units (feet, meters, MPH, KPH, etc.). 

Note:  Works with PerfectFlite Firefly altimeter only, not intended for other altimeter types.  Firefly altimeter sold separately.