HRM help

loombeav

I need some opinions. I use to have an HRM that did not have a chest strap, when I work out at Curves I use a smart card that tracks my HR and intensity level and tells me calories burned. That HRM usually was over Curves system by about 50-75 calories. I kept hearing how HRM's aren't accurate unless they have a chest strap, so I got one. It's a pain in the butt and very confusing to set and for the last month when I've been working out it's said that my calories burned has been very low. I keep my HR up between 65%-85% for my entire work outs and it's been reading about 100 calories less then the Curves system, on average a 44 min work out only burns about 300 calories according to it.
So today I was checking the settings to be sure I had my weight in there right and saw that I had it set on low intensity. So I changed it to medium and went for a walk/run. Tuesday when I went I ran for longer then I did today and it said I burned 225 calories, today I walked the same distance in the same amount of time and it says I burned 449 calories. Both Tues and today I carried 2lb dumb bells, Tues I ran for about 1/2 the time today I only ran for about 2 mins, but did arm workouts the entire time.
Which calorie burn do you think is more accurate. I do not want to over estimate my calories, but it's very discouraging when I do what I think has been a killer workout and I only burn 300 calories.