Last Saturday evening I read the users booklet for my Polar heart-rate monitor and discovered that it saves the highest and lowest heart-rate during a workout session. So, this morning I ran a test to compare the reading on the monitor with the maximum value saved. I've been suspicious that the value displayed is an average of some kind, and if so, that value might be less than the maximum heart rate that I achieved during the workout. After running 3/4 mile warm-up at a heart rate of about 90, I ran a half mile split at a pretty fast pace. When I finished the half mile, the monitor gave a value of 112 (my 80% of max is 119). I then checked the maximum value that was saved, and it was also 112. Thus, if any averaging is done, it is probably a moving average over the last few readings, which are taken at a rate of some fraction of a second. The monitor display is uppdated every second or so, and since only a few readings are probably used in the averaging, the averaged result would likely be the same as the displayed value. I thus concluded that the HR monitor can be trusted to give a good value of my HR while running. I did this, because some runners have had problems getting good values from their HR monitors.
I then ran a test on the "10-second measurement" that I described on Saturday. I ran a rest pace and used the HR monitor to see how much my heart slowed down in the first 10 seconds after I stopped (my heart slowed 2 beats). I then ran the rest pace until my HR stabilized, and then I stopped and manually counted the beats for 10 seconds. I added 2 to that value to compensate for my heart slowing down. I compared that value with my HR rate as measured by the monitor divided by 6, and the two values were the same.
I finished my workout with a 2-mile run at a comfortable pace yielding a heart rate of 90. The temperature during my workout was in the mid 50s (F). A really great spring day!