I'm using Clearblue Advance Digital.

Shows a "O" for low fertility.
Shows a blinking for high fertility
Shows a solid for peak fertility.

Using the OPK, I got 2 days low, 3 days high and 1 day peak (the test says to stop testing when you get the peak as a result).

Now does that mean my O'day was the "peak" day? Or the first "high" day? Or the last "high" day?