The F4™ is the first women's specific unit from Polar, combining all the necessary heart rate features with a new, slim design. The F4™ includes the popular Zone Pointer feature that helps keep you in your Target Zone, and OwnCal® to track the calories you burn during your exercise. With stopwatch and convenient button free operation, the F4™ is a valuable fitness tool. Available in four color options. Black Thunder is the Men's version of the Polar F4.Polar exercise featuresWir