I'd try taking your pulse yourself while you are on the machine if you can, I know when I'm on the elliptical machines the monitor is usually really low or jumps all around so I don't pay attention to it. I just check my pulse once or twice while I'm on the machine if I feel like it.
You may want to take into consideration your perceived exertion as well. Here is an article on it: http://sportsmedicine.about.com/cs/strengthen ing/a/030904.htm
As you know, there is no exact science to calculating calories burned since we are all different...this might help.
Also, 105 seems VERY low to me given that you are sweating after 7-10 minutes. I am 35, 5'-2 and typically get up to 130-140 within 5 minutes and I'm just starting to break a sweat on the elliptical. There's a possibility you may be over-training a bit? I once had trouble getting my heart rate up and was told by a fitness instructor that I needed to give myself a break. It worked! I started doing the cardio (elliptical or walking/jogging) every other day and weight training on the other days. It was much more effective. You may want to consult with a fitness expert (maybe someone at your gym?) It's hard when you're really driven to lose weight to have someone tell you to back off, but you have to do what's most effective for your body.
The bottom line is that I wouldn't rely on the exact numbers on the chart and would try perhaps mixing up your routine a bit. It sounds like you're making excellent progress though, so maybe you don't need to change a thing and don't worry about what the fat-burning numbers say.
i suggest buying a POLAR heart rate monitor...i don't think you could be at 105 heart beats per mminute when you are covering 3 miles in 30 minutes!!!
the polar heart rate monitor comes with a manual that explains all about heart rates and determining when you personally are in your fat burning versus aerobic zone.
i love love love mine and it is the $50 basic one.
The Heart Bit Rate depends on your fitness level. There are a number of formulas which you can use to calculate your Target Heart Rate. For weight loss you shoud do cardio at 60% to 80% of your Target zone (depending on your fitness level) for at least 30 minutes exluding the warm-up and cool-down.
Actually when I'm on elliptical my pulses starts from 105 and gradually goes up to 150-157 after 20 minutes...And I usually stay in for 45 minutes or so. If your elliptical shows maximum 105 there is a possibility that the HR monitor is not working properly.
There is a simple test in which you can find out whether you're exercising in Target zone or not. This test is called Breath Test and it says that while you're exercisiong, if you cannot complete a simple sentence without breathing in between this means that you're in the target zone. If you can talk easily and have a long conversation, then you're below target zone. And if it is very difficult for you to complete one sentence and you have to stop many times to breathe, this means that you're overdoing and you have to reduce your workout pace.
I have yet to use a piece of exercise equipment that reads the correct heart rate if I don't have my HRM strap on and if it picks it up. We have an elliptical - brand new less than 2 weeks old and it doesn't even register right and doesn't pick up my polar strap right either. The recumbent bike does better and the treadmill - guess its the brand of elliptical.
Also you got to think how many paws have been on those handles depositing skin cells and grease and oil and who knows what else and that has to effect the sensors plus the sensors are not able to be recalibrated like a scale for example.
So what I am saying is don't trust the machine. LIke others have said invest in a HRM or go by the perceived rate of exertion. Also if the machine doesn't have the capability of eentering your age weight height and sex the calories you burned aren't even going to be close.