Difference between calculated Triaxiality and the triaxiality(TRIAX) directly from Abaqus.

Hello,

i am trying to compare the results between calculated Triaxiality and the Triaxiality(TRIAX) field output from Abaqus.

Here Triaxiality calculated using formula Triaxiality  =  -(PRESS/MISES). Which is a same formula used to calculated TRIAX.
Let me know what could be the possible reason for this difference.
Thanks in advance.