I didn't understand how TBits.NotBits works. Consider the following code: b:= TBits.Create(NRECORDS); b.NotBits(b); or more clear: b:= TBits.Create(NRECORDS); b.Clearall; b.NotBits(b); I supposed that all bits of b will be 1. What I obtain is that all bits are 0. fpc 3.0.0 win64 Am I missing something? Thank you. Andrea Mauri