Is chest HRM more accurate than a wrist one?

Accuracy of what, it's intended function, monitoring your HR?

Chest strap.

Or side purpose of estimating and calculating your calorie burn?

Depending on your workouts, may not even be HRM is best for that.

As Michele indicates, not for weight lifting.

If walking 2-4 mph or jogging up to 6.3 mph, a step based device (FitBit, BodyMedia, JawBone, ect) can actually have better chance of calculating calories better.

Accuracy of what, it's intended function, monitoring your HR?

Chest strap.

Or side purpose of estimating and calculating your calorie burn?

Depending on your workouts, may not even be HRM is best for that.

As Michele indicates, not for weight lifting.

If walking 2-4 mph or jogging up to 6.3 mph, a step based device (FitBit, BodyMedia, JawBone, ect) can actually have better chance of calculating calories better.

For estimating calorie burn in hard-to-measure workouts such as a trampoline class, a kick-boxing class and a micro-toning class.

In that case you'll need one that has the very important VO2max stat, and Polar has self-test to estimate it decently, along with HRmax.
The are still calculated assumptions, and then those are used to calculate calorie burn - but a whole lot more chance of being decently accurate than the cheaper Polar models or other HRM's with no such stat.

The cheapest Polar I found with that required stat and self test to estimate it - RS300X.

Accuracy of what, it's intended function, monitoring your HR?

Chest strap.

Or side purpose of estimating and calculating your calorie burn?

Depending on your workouts, may not even be HRM is best for that.

As Michele indicates, not for weight lifting.

If walking 2-4 mph or jogging up to 6.3 mph, a step based device (FitBit, BodyMedia, JawBone, ect) can actually have better chance of calculating calories better.

For estimating calorie burn in hard-to-measure workouts such as a trampoline class, a kick-boxing class and a micro-toning class.

In that case you'll need one that has the very important VO2max stat, and Polar has self-test to estimate it decently, along with HRmax.
The are still calculated assumptions, and then those are used to calculate calorie burn - but a whole lot more chance of being decently accurate than the cheaper Polar models or other HRM's with no such stat.

The cheapest Polar I found with that required stat and self test to estimate it - RS300X.

Thank you. Now I just have to do some research to understand what you said

What VO2max is - http://www.brianmac.co.uk/vo2max.htm

HRmax - max HR beats your heart could go up to, not that you'd even want to always be trying to reach it, but it then tells HRM how intense your workout was. Doing a workout at 70% of HRmax is much more intense and burns more calories than a workout at 50% of HRmax. Genetic, and exercise as you age prevents it from lowering compared to not. Higher or lower no indication of fitness, some have diesel hearts, some have 2-cycle hearts (slow & big, fast & small).

VO2max - how fit you are, tells HRM how intense you worked out for your fitness level, besides the HRmax. So if you did that 50% of HRmax workout, if you had a low VO2max because of being unfit you'd burn less calories than if you had a high VO2max because of being fit. Being fit, you'd have to go run faster and harder to hit that same 50% HRmax, being unfit might be walking up a slight hill. Genetic too, but can improve it up to a point.