These fields determine the default settings for the Record History and Show Trend fields on the Properties tab.
Default for "Number of Days"
Determines the default Number of Days for the Record History.
Default for "Show Trend"
Determines if Show Trend is enabled or disabled by default. When enabled, the trend is only shown when the task’s Record History is enabled.
Enable "Record History" for All Tasks
Determines if Record History is enabled or disabled for all of the tasks by default.