Hi! I've been using my Wahoo TICKR X chest strap with the wahoo fitness app for a while. To be honest, I always suspected my calories in the wahoo fitness app a little bit high. Now I have an apple watch. I did several tests. The last one was today and I'll talk about this one. What I do : I connect my chest strap to my iphone (bluetooth) and I start my run using the wahoo fitness app At the same time, I start an "Outdoor run" on my watch. One thing I can say, I'm REALLY impressed with the apple watch. I looked at my HR on the watch and on the app every minutes or so. Every time, the HR is the same on both the watch and the chest strap (less than 5 heart beats difference). But the results...really not the same ! Both the watch and the app have my age, weight and height correctly set. So the way calories are count are really different. For the same session : wahoo :258 calories watch : 136 active calories, 38 resting for a total of 174. Now, what is the correct way to measure calories. Only active as apple does or total as almost all other companies do ? Do you know other product that only count active calories (like apple) ? But even with this, the watch total is significantly under the wahoo app... Anyone using the same products as me ? From what I understand, active calories make more sense than "total". Why other don't do that ?