How reliable are the calorie guidelines?


So I just wondered how reliable the estimated calories you are supposed to burn are on each work?

I understand its going to be completely different for everyone, but I recently bought a fitness watch (a VERY cheap one) and what should have been a 200+ calorie workout, my watch was telling me I had burnt about 36!

Made me feel a little discouraged, so would be nice to hear that the calories on the workout is more like it!