conflicting HRMs

Erg, I think I know the answer to this, but lets see anyway. Today I started walking again on my lunch....it's been a long time since I walked for excercise, and even though I have been working out (jogging on treadmill and biking) for the last 4 years, it's been pretty inconsistent for the last few months, I haven't done ANYTHING in a few weeks and I've gained some weight back over the last few months.

So despite working out in other ways, the walk was a little hard for me because I'm working muscles that haven't been worked, my shins hurt and my feet cramped a little, this is normal for me when I haven't walked much. I used to use a RBK precision XT HRM, but I felt it wasn't giving consistent results (one minute it would say my HR was 148, then it would blink 0 for a minute or so, the back in the high 130's/140's, etc. So I bought a polar F4 two years ago and haven't used the RBK one since.

Today I used it since I figured I'd leave this one at work for my walks.....right away it said my HR was 120, and then flitted between 122 and 142 the entire walk. Like I said, I was working hard on my walk, but that's where my polar says my HR is when I am jogging on the treadmill or biking. I just can't beleive I burned 348 calories on a 30 minute walk.

I know the obvious solution is to use my polar tomorrow, but what about today, how should I log it? Also, I did reset my info on the RBK since I've aged a couple years and gained some weight since I last used it, but is there some other setting that I maybe don't have right that could be affecting what it says my HR is?