Designed for the Researcher and Professional Trainers - The new S810i is like having a sports research facility at your disposal. Infrared technology links this powerful HRM to your PC (optional IR interface required). R-R Variability, a Polar exclusive feature allows you to test your stress levels and detect overtraining. This is the perfect unit for a research facility or advanced coaching programs. Please Note: Your PC must have an infrared window in order to download without the use of a separate IR Interface. If not you will need a Polar IR USB Interface. Main Features: OwnIndexS™ - Measures your VO2 max OwnCal™ - Tracks nutrition expenditure OwnCode™ - Personal transmission feature Exercise Set™ - program the parameters of five key workouts (TZs, Timers, Recovery) Downloads data to your PC in seconds with the optional IR interface Includes IrDa which allows transfer of data from a PC using infrared communication. View heart rate as a % of Max hr 3 Target Zones and Timers Average and Recovery Heart Rate Interval Trainer Lap Splits with avg. Hr New ultra-thin chest transmitter Low battery indicator on watch receiver New, easy to use programming logic Full function stopwatch and everyday watch Two year warranty Stores 99 Files File Storage Capacity 60 sec. - Approx 200 hrs. 15 sec. - Approx 120 hrs. 5 sec. - Approx 44 hrs. (Storage capacity dependent on features in use) Polar Precision Performance Software