The Data Distribution window shows the heart rate zones, heart rate, speed, cadence or power readings as a bar graph, showing the amount if time spent in each 'band' of readings throughout the HR range. The width of the bars can be set to 10, 5 or 1 BPM in the 'Preferences' Dialog.
To view the data distribution graph, select 'Data Distribution' from the 'View' menu, or click the 'Data Distribution' button in the toolbar.
To switch between views of the different data, click the buttons in the toolbar.