When you schedule an In-App campaign, it will be displayed according to the trigger you have chosen such as New Session, As Soon As Possible or based on a custom event.
However a Synched device isn’t equal to a Displayed device as you can see on the chart pie on the metrics page of each of your In-App campaign:
It is the number of single devices that were targeted by the campaign and have dowloaded it locally.
When users who match the predefined targeting conditions start a new session of your app, Batch's SDK will retrieve all the information related to the campaign and count them as synced devices.
It is the number of times your campaign has been displayed.
It means that users that were targeted by the campaign dowloaded it successfully and triggered the message according to the display event that was defined.