How accurate are the heart rate monitors on the handlebars of exercise machines?

for example, handles of bicycles and treadmills. Is it really a very accurate to measure heart rate through your hands?

so a little depends on the machine you are using, because if the exercise machine is more modern than it is more likely to be more accurate. find the machine on the line, and some people may comment on how they liked the machine, and the accuracy of measuring your heart rate. I have a tread mill and it works very well, and probably should be used more often because football is coming soon! : D

Animated heart rate monitor – electrocardiogram