HRM's & Metabolic rate?

Hi,

I'm wondering if anyone has any experience/suggestions for using a heart rate monitor to help determine basic caloric needs. I feel like I'm having a hard time getting a handle on how many calories I need per day. I just purchased this heart rate monitor, which has a feature that "measures" how many calories burned. I'm sure it's just applying some kind of multiplier to the heart rate it's measuring, which I'm sure is not very accurate. Can anyone suggest any formulas I can use to tweek the data the watch gives me to include variables such as gender, age, weight, height, etc.? Or any ways to use basic heart rate data to calculate the same, at least to get a ballpark estimate of my caloric needs?

And one other question.... when trying to loose weight, is it best to keep caloric intake relatively constant over time, regardless of activity level on a given day? In other words, some days I may have longer workouts and burn more calories, other days I'll have shorter (or no) workouts, and burn less calories. If my goal is to loose 1 - 2 lbs per week, am I better of trying to adust for 500 - 1,000 calorie deficit per day, or a 3,500 - 7,000 calorie deficit per week, and keep calories per day more or less constant over the course of a week? The reason I ask is, when I've tried to maintain a calorie deficit on those lower activyt days, I always find I feel hungry - I think my body is accustomed to a certain amount of food, and when I restrict beyond a certain point, even if I'm not burning as many calories on that day, I just feel hungry all the time.... Thoughts???