Heart rate monitor confusion

I had plenty of time before tonight's ride so I thought I'd wear the heart rate (HR) monitor that came with my Polar cycle computer.  Normally, I don't bother with this; in fact this is only the second time I've worn it.

If the computer can't detect its presence then in the bottom left corner it displays the average MPH in fairly large digits; which is the normal mode for me.  However, if it can detect the HR monitor then current HR is displayed.  I forgot this and when I looked at the numbers I subconsciously inserted a decimal point between the 2nd and 3rd digit and thought my average MPH was really good; then I realized...