Are HR Monitors accurate?

I have a Polar F7 which I love wearing during workouts because I use it to determine the rest time between sets (once my HR is below "range", or 120bpm, I start the next set), I am also using it to calculate my calorific expenditure of my workout. Thing is, I am not sure how accurate it is. It says I am burning up tp 1,100 calories for my 1 hour workout! Sure, workouts are intense but does it really burn that much energy? Would like to hear other people's opinion on this.

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resting test to get VOmax? I draw a blank right there..

My take is that if I am just sitting there doing bicep curls, of course the calorie expenditure on my device won't be correct. But for compound exercises with minimal rest, shouldn't the reading be more or less accurate? Btw I am taking the calorie amount to be the total amount, that is, including the BMR.

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I have the FT7 too and have had it since Xmas. Pretty good when using machines I notice if I use the machines heart rate there will be a 2 - 5 beat variance if that. So its seemingly accurate, assuming the machine are accurate.

However I sweat like a horse on the Melbourne cup event when working legs especially heavy squats, so it seems my calorie expenditure is huge, however I don't trust this, and I still only use it as a rough guideline even when doing aerobic/cardio exercises.

If you have an arrhythmia they skew the results.