TBN (Total base number) indicates the oil's ability to neutralize acids formed during combustion or oxidation. A high TBN means good protection against acid formation, while a low TBN indicates that the oil is starting to lose its protective properties.
This analysis is also carried out by titration, but here an acid is used to neutralize basic components in the oil.
The result helps the customer assess whether the oil still provides adequate protection or whether it is time to replace it. Particularly relevant in engines running on high-sulfur fuel.