I am using Avogadro 2 in classroom installed in S.O. Linux. I realized that by using the “Measure” tool we get the sign of dihedral angles reversed. I mean, if angle (I,j,k,l) is read in clockwise sense the sign appears negative and, following the current rules, it should be positive. However, I have checked an older version (Avogadro 1.2.0) installed in a S.O. Windows computer and it is O.K.