On first installation, you will see a box showing the loading progress on the screen, let the loading progress finished otherwise the database is not fully loaded. You might need a few seconds until the database is fully loaded.
If you accidentally close the apps when the loading progress if not finished, go to:
Setting – Apps – Petroleum Dictionary – Clear data
Reopen the petroleum dictionary and wait until the loading progress reach 100%.
1. Offline dictionary
2. Super fast search
3. Word suggestions
4. Small size apps