how comment in history is related with track history properties in Itemtype.
Administrators can specify History Templates for each ItemType in the database. This History Templates can keep track of different events that may happen to an item such as Add, Update, Delete, etc. Each of these actions can have different comments associated with them. For instance, you may want to track the old and new value for an item when it is Updated.
You can find more information about this history tracking under the Just Ask Innovator menu which you can access from the main grid of your instance under Help > Just Ask Innovator.
Aras Labs Software Engineer