Want to be accurate with your calorie burn??

You are assuming the HRM is the most accurate but you have no way of knowing. All methods are estimates.
Some things that affect the accuracy of HRMs
Limitations of Heart Rate Monitoring

However, assessing PA (Physical Activity) based on HR data has some inherent limitations that must be acknowledged:

• Established relationships between HR and AEE (Activity Energy Expenditure) are lacking for many lifestyle activities.

• The linear HR vs. VO2 relationship applies to moderate-intensity activity but is nearly a flat slope during low-intensity activity, resulting in a low correlation between HR and EE (Energy Expenditure) during sedentary and low-intensity activities.

• Due to inter-individual variability HRM data is best applied to groups.

• Numerous confounding factors affect the HR response to PA and therefore the HR vs. VO2 relationship.
These include high ambient temperature or humidity, time of day, emotional state/stress, fatigue, hydration status, food, caffeine and nicotine intake, previous PA, illness, body position, mode of exercise and use of limbs.

• Training status will also affect HRM data, as a less fit individual will elicit a higher HR than a more fit individual at any given VO2.

• Changes in work rates require a 3-5 minute adaptation period for the HR response to stabilize at that exercise intensity. Therefore, the exercise test protocol must allow sufficient time for the HR to reach steady state.

• HR monitors are subject to electrical interference (i.e. computers, hairdryers, car engines, etc) which result in either spurious high or low values or momentary loss of data, and the affected data needs to be either removed or replaced by the mean of the surrounding HR values.
http://www.myfitnesspal.com/topics/show/773451-is-my-hrm-giving-me-incorrect-calorie-burn



I am not anti HRMs, I understand people find them useful, however, I do think that their accuracy is highly overstated here. Many people have run into issues by blindly following their HRM without understanding the limitations. I feel bad for those who feel they must buy one to be successful when it is not within their means.
Besides, your numbers aren't too off of the estimates.

Having a heart rate monitor will get you closer than a calculator I am sure it is not spot on..but a heck of a lot better than wondering

The amount you burn will depend on how much effort you put into it...and a standard calculator can NOT determine that

^^ I stated I am sure the HR monitor is not spot on either..but it is a heck of a lot better than a standard calculator

Also - while "some" are not far off...if you have a bad day such as I did today but only put in half the effort everyday..at the end of the week it makes a difference as those "bad days or lack of effort" will add up

Again, you assume the HRM is most accurate. I have seen some people with hugely inflated burns because of improper use. For some activity, the standard calculator is just fine.

ANother great blog on accuracy.
http://www.myfitnesspal.com/blog/Azdak?month=201201
http://www.myfitnesspal.com/blog/Azdak

I agree, used mine for the first time yesterday whilst doing high impact aerobics, worked out i burned roughly 620 cals as opposed to the 340 odd estimation. Looking forward to using it again tonight in my step class