The Frequency List menu (above) allows you to change the active character frequency list. The active list is the one that appears when you click on the Character Frequency tab (below) of the Reader.
In the Settings dialog you can specify whether to include additional details when the lists are displayed. These lists are designed to help you focus on learning characters that occur most frequently in your reading.
Refer to the page, Character Frequency Lists, for full coverage of this feature.
See the February 2018 updates for
← Chinese Toolbox and Toolbox Coding →
especially the new Chinese Toolbox 188.8.131.52.