Equivalent von misses stresses on MSC Mentat

[yenerme]

I am a user of MSC Mentat.In one of my post processing operation i have realized that the values obtained by theorotical 'von misses' formulas doesn't match with the marc result named as 'equivalent von misses' however this theorotically calculated value is exactly same as the marc result named as 'equivalent stress'
After all that i had a conclusion that 'equivalent von misses stress' and 'von misses stress' are different things.
I know the formula of von misses but i couln't find any formula for equivalent von misses stress.
Is there any one who clears that contraversy.
Regards