Question about stationary bike.

I rode my stationary bike for 10 minutes (not that long, I know). I logged it in my activity log and it said I burnt like 46 calories. The bike said I burnt 166. Which one should I go by?

It all depends. Both can be reasonable but you have to consider factors such as your weight, and the speed you were going at while riding.

it does depend a lot on your weight, the resistance, your speed, muscle mass, cardiovascular fitness, etc.  but i'll use me as an example: i'm 5'7, 145lbs, 28yrs old, i'm fit, i burn around 450calories in a pretty rigorous hour on the stationary bike (according to my heart rate monitor).  that's about 80 calories in 10 minutes.

Since the stationary bike is probably not programmed with your weight, height, etc. I would go more by what the activity log said.  I am 36, 141 pounds, and 5'8" and my HRM is almost exactly what my activities burned says - about 110 every 15 min. on the stationary bike going about 88-94 rpms.  It is common knowledge that the calories burned on the equipment can be as much as 30% off compared with your actual numbers.  So much is dependent on your fitness level, target heart rate, and other stats, and the equipment is usually calibrated for a "typical" person. Of course, we know that there are few "typical" people out there!! 

I will log what's on your stationary bike.  Each bike is programmed to calculate your workout and some do have pulse sensors.  Even if they don't, I believe it has better tracking of your workout rather than some equation.