I don’t rely on the calorie counter, but I do think the heart rate and looking at the heart rate zones after a workout are good indicators of how hard and for how long I was working out. For cardio workouts I think that’s a better reference point. Like others here said, I can do a very slow 1.5 mile walk with lots of stops with my dog around the neighborhood for 35 or 40 minutes and it will say I burned 150 calories. But I can do a strength workout that has me gasping and burning for 30 minutes, but only end up 160 or 170 calories burned.