A:Answer JJ,
Have you fully explored your app? You should be able to select the heart rate and see your chart, then get a weekly, monthly, 3 month etc view. This can be expanded so you see a chart with your highs, lows and all of the middle.
If you are looking for just a heart rate monitor, or one to catch almost every beat, read the literature from the company - they tell you to go get a chest strap type. I have had one of those, and all though they are accurate, they can be uncomfortable. The Fitbit is a motivational tracker, not a Heart Rate monitor per se.
Good luck with your fitness goals.