calories burned

So I finally got a new HRM last week. Yesterday I used it when I was on the elliptical for 30 minutes. I had been estimating that I am burning 300 calories during that particular workout. At the end of it, I checked my HRM and it only had 233! I was so bummed! This morning I had my PT show me what to change to get the burn I want. Then he proceeded to increase my routine with him as well! Looks like I've make it to the next "level" in my workout routine! I'm excited since i will now see more results!