Synchronization reports and logging
When a synchronization is started by clicking the Sync Selected button or while running a MultiSync with the option Show pre-synchronization report activated a report panel will popup over the current document window: here you can click the OK button to make the synchronization process commit its data to the calendar files and ultimately synchronize them, while clicking the Cancel button the synchronized data will not be saved and the calendars will remain untouched.
In the aforementioned report panel you can see how many items will be affected by the current synchronization: clicking on each small button reporting either the number of items before/after the synchronization or the number of synchronized/copied/deleted items, a related secondary panel will open to show a detailed list of the affected items, reporting the start date, description and kind (event or todo) of each item.
This option also affects the Calendar Copy synchronization method, because when the Show pre-synchronization report option is enabled and you already have on the destination folder a calendar file with the same name of the source calendar a dialog will show to ask confirmation, otherwise the existing file on the destination folder will be overwritten without prompting the user.
Every time a synchronization is run all of its details, like the names of the involved calendars, the synchronization method used and its result, combined with a list of the items modified by the synchronization, are saved by default in a log file inside the ~/Library/Application Support/iSynCal folder of the user running iSynCal. You can browse the log by either clicking the Show Log button in the iSynCal toolbar or choosing the related menu item.
Moreover, in the iSynCal preferences you are allowed to modify some synchronization log settings to suite your needs: you can activate or deactivate at all the logging feature (it's active by default) or limit it to log a certain number of synchronizations (50 by default, the older entries are removed when needed). Additionally you may enable or disable the verbose log mode (enabled by default), which allows you to store in the log file a detailed list of the items modified by each synchronization, reporting their start date, description and kind (event or todo).