RobotStudio event

Energy consumption

Hellow everyone:

I have getting ABB robot energy consumption by using webservice,but The total energy consumption directly getting webservice is not equal to the total energy consumption of all the axes?

And the every axis' energy may be minus,what is meaning?

The total energy consumption directly getting webservice is equal to the total energy consumption of all axes only if the energy consumption of the axis is negative?

Does anybody know why that is?