Diamond DA 40 Flight Manual page 174

Performance DA 40 AFM
5.3.2 TABLE FOR SETTING ENGINE PERFORMANCE
NOTE
If the Long Range Tank is installed:
Auxiliary fuel below 3 US gal cannot be indicated by the
system. If a fuel indicator shows 16 US gal and the auxiliary
fuel indicator reads 0 US gal on the same side, for in-flight
fuel consumption / flight planning a fuel quantity available of
16 US gal must be assumed.
Page 5 - 4 Rev. 8 01-Dec-2010 Doc. # 6.01.01-E