What is Offline Mode?
DiveTab uses Offline mode, also known as Airplane mode, to access data when you are without server or internet access. For offline use, DiveTab downloads cBase and cPlan data locally, and parts are loaded into memory to service dives.
How to indicate a data area for offline use
Include the offline = true tag to indicate that a data-area is intended for offline use. The entire data-area is then downloaded. This action stores the cBase locally on your device and preserves all functionality offline.
Use a smaller cBase for data areas intended for offline mode because larger cBases take up space and slow your device. Offline cBases can be a maximum of 400 MB, and dive results can be a maximum of 200 MB.
NOTE: A 64-bit iPad is required to use offline mode with the DiveTab application.
Offline mode processes
A Sync operation downloads cBases and cPlans for offline use, and a lightweight version of Spectre runs local Dive and QuickView requests. The lightweight version of Spectre, divetab_assist.exe, must be in the same location as the DiveTab executable. The DiveTab client first tries to access previously cached data. If there is no result from the cache request and offline mode is enabled, DiveTab tries to access offline data.
The preload=true tag determines dives in advance to make tables load faster in the interface. Avoid using preload=true if dive results exceed 200 MB.
When offline files are added, changed, or removed, then all offline files are removed. Perform another Sync to regain these files.
Example
Here is an 
example of a data-area configured for offline use:
CAUTION: Different versions of DiveTab support different iterations of Offline Mode. This documentation refers to the latest software.
See also Using DiveTab Offline