The top photo shows data collected by my AW3 and data calculated by Apple Activity App's Indoor Cycle program. The bottom photo shows data collected by Polar H2 chest strap and keiser m3i bicycle which uses magnetic resistance. The HR at any given moment was usually within ±2. Average HR was 156 vs 153, Apple's number is 3 points higher. The calories burnt were 228 Cal vs 204 Cal. Apple's estimate was about 10% higher. Overall, I am quite impressed by the accuracy of AW3 HR sensor. I do not enjoy wearing the chest strap because of obvious reasons. The watch on the wrist is much preferable. If the m3i bike app programmer can incorporate AW HR monitor into their app, I would not have to wear the chest strap at all. I will contact them someday about this. *I started the exercise bike app after I started pedaling so the duration has slight discrepancy. The app is on iphone and it does not start automatically when I start pedaling. The Activity app was programmed on my AW3 with the target of 225 Cal to burn.