Synchronizing Behavior
In addition to the Synchronization Method and Direction, you can also set various combinations of the following checkboxes, located in the Options drawer, to substantially change the behavior of each synchronization task.
Synchronize matching events/todo already existing in both calendars [Opt-S]
Activating this option will cause the synchronization of all pre-existing events and todo between the two involved calendars. This means that all items already existing on both calendars and having the same UID will be synched, taking into account the item's latest modification date to establish which item is most recent (except when Ignore last modification date is active).
Activate this option if you want the existing items' modifications made with iCal on one calendar to be applied, while synching, also on the other calendar.
Ignore last modification date [Opt-M]
This option is available only when using the One-Way synchronization method and only if Synchronize already existing is active.
Activate it if you are sure that a given calendar contains the most recent items or if, for any reason, you want events from the source calendar to override the correspondent ones (having the same UID) on the other side, regardless if the items on the source calendar could be earlier than those of the destination calendar.
Copy new events/todo between calendars [Opt-C]
Activating this option will cause the new events and todo to be copied between the two calendars involved in the synchronization process. All items present on a calendar but not having a correspondent on the other one will be copied there.
This option must be active if you want the items added on a calendar to be copied to the other one while synching.
Synchronize events/todo deletions [Opt-D]
Running a synchronization with this option active iSynCal will also synchronize the item's deletions. For example, if after a synchronization you use iCal to delete some items from one (or both) of the previously synchronized calendars then iSynCal will delete the correspondent items in the other calendar during the next synchronization between the same calendars pair.
If Synchronize events/todo deletions is instead disabled, deleting some items on one side would not trigger a sync deletions event so the correspondant items would not be deleted on the other side and will stay there untouched by iSynCal unless you manually delete it; even enabling Synchronize items/todo deletions later and running a further sync would not sync such items' deletion because iSynCal records the state of each calendar items at the end of each synchronization and only sync the changes occurred between the last sync and the current state.
To keep track of the items present the calendars after a synchronization is run, iSynCal mantains its own database where it keeps a list of the items' UID contained in each synchronized calendar. Such a database is stored only on the computer running iSynCal into the file
~/Library/Application Support/iSynCal/ItemsHistory.plist
and is updated every time a synchronization is run. It is hence necessary for such items to have the same UID on both calendars to properly synchronize their deletion; this only happens when they are present on both calendars because of a previous synchronization (see How does the synchronization process work).
The UID list database is searched by iSynCal using the calendars' unique ID (automatically generated by iCal when a new calendar is created), so you may safely rename a calendar (remember to revise your MultiSync documents if you do so).
Anyway don't be confused ... the access to the above mentioned database and its management are completely transparent to the user, they are briefly described here just for completion and to give you some hints about using iSynCal. All you really need to know is that when this option is active and you delete some items on a previously synchronized calendar the same deletions will be made in the other calendar during the next synchronization.
Check and remove duplicates [Opt-R]
Some users reporting duplicates in their calendars requested this feature, so here it is. This option is based on a simple assumption: it's unlikely to have on a calendar two events with the same start date/time and the same description. Enabling it iSynCal will check both calendars at the end of the synchronization process to find such items: in case they are found it will remove the earlier and keep the most recent.
This option is off by default because under normal conditions you should never experience duplicated items on your calendars, unless you have duplicated an event/todo either you have manually entered the same item on two different Macs.
This could also happen because you have not used iSynCal to copy a calendar between Macs/users, as described here.
In other rare cases it's not yet clear how and why this event occurs, but it seems related with iSync, particularly when synchronizing with some PDAs the same calendars that are also synchronized using iSynCal, or with some strange iCal behaviors, when it arbitrary changes the items' UID for unknown reasons.
Synchronize/copy event items [Opt-E]
Activating this option will cause all Events to be synchronized and/or copied between the two calendars involved in the synchronization process, depending on the synchronization settings above.
Synchronize/copy todo items [Opt-T]
Activating this option will cause all ToDo to be synchronized and/or copied between the two calendars involved in the synchronization process, depending on the synchronization settings above.
When this option is active the synchronized event/todo's alarms will be synchronized too, otherwise each calendar item's alarms will remain unchanged after the synchronization. Please note that when this option is disabled the alarms are not copied at all while copying a new event/todo to another calendar, thus the new event/todo will have no alarm set on the destination calendar.
It may be useful to disable this option when multiple users are synchronizing their calendars and each user wish to retain his own alarms settings, either no alarm at all, in his copy of the synchronized calendars.
When this option is active the synchronized event/todo's notes will be synchronized too, otherwise each calendar item's notes will remain unchanged after the synchronization. Please note that when this option is disabled the notes are not copied at all while copying a new event/todo to another calendar, thus the new event/todo will have no notes set on the destination calendar.
It may be useful to disable this option when multiple users are synchronizing their calendars and each user wish to retain his personal notes, either no notes at all, in his copy of the synchronized calendars.