User-friendly, lightweight multisport watch with GPS Garmin FORERUNNER 45S OPC with an optical pulse monitor that estimates heart rate t the wrist. Forerunner 45S OPC belongs to the more simple range of GPS watches with small-size, low weight, but enough of a performance required by beginners and intermediate runners. One of the biggest advantages of Forerunner 45S OPC is a touch screen that works well even in the rain and a colourful screen with an excellent readability in the sun and back light for comfortable use even in the dark.