@garyjnj1, if you click on "More Detail" you'll see the data behind the graph. Without reviewing your account, I'd assume the system ran and you received some rain or ran the zone manually as we'll only water up to 100%.
To learn more about Moisture Levels, please see this support article.
The watering depth in inches is derived from your root zone depth and available water (soil type), which can be found in the zone's advanced settings.
To learn more about the advanced zone settings, please see this support article.
Hope this helps!