For example, the following two functions should returns the same result, but they don't.

=VDB(100, 10, 13, 2.3,3.3,2,TRUE)
=DDB(100, 10, 13, 3.3,2)

The first gives 10.51, the second 10.48. This is observable for every not integer period passed to DDB (4th parameter). Manual testing shows the VDB result to be correct.

Anyone knows what DDB is doing and why?

Thanks,
.luca