The Preferences toolbar icon becomes available, allowing you to customize the settings for the chart. Refer to the Preferences section earlier in this chapter for more details. In addition, you can select the context menu.

You will notice that the Time Of Day area of the Preferences screen is not available. The ability to select a single time-of-day does not make sense with this particular chart.

Multiple instances of this screen can be displayed concurrently, allowing you to compare before-and-after charts by modifying the preferences, such as the date range, for each screen.

As with the History View Chart, the Day View Chart displays a running average, calculated as the mean of selected readings within each two hour time period. This running average will show the trend for your readings.

As well, a number of statistical values are displayed. The average is indicated by the line across the center of the chart, while the lines above and below this average line indicate a distance of one standard deviation on either side of the average.

The standard deviation is a population statistic if all of your readings are selected; however, if you have set the Preferences, the standard deviation is calculated for the sample.

The range bounded by one standard deviation in either direction from the average will contain approximately 80% of your readings.