Polar G3 GPS Sensor Set 2" high 4" wide Wristband Size : 8.5  . NOTE - Measurements taken from the LAST HOLE to the END OF RUBBER next to buckle (not from end to end). Wristband Size : 8.5  . NOTE - Measurements taken from the LAST HOLE to the END OF RUBBER next to buckle (not from end to end). Speed and distance GPS sensor with adjustable armband and user replaceable "A" battery Designed for indoor/outdoor crossing training Calculates speed within 0 to 18.3 miles per hour Operates on 5kHk transmission and uses SiRF Star III technology for accurate GPS readings Compatible with Polar RX300, FT80, and FT60 training computers