In the circle it says 86 high and 5 low which looks about right. The lowest you had was to the far left in the graph which looks like 5. That is also the lowest value you can have.The highest was when you woke up (around 7 in the morning) and it looks like around 86. Hold the finger on the graph and you will get an overlay with the value in the graph.
this is just an outright bug 