In this timeline , Sage served as Professor Xavier 's Executive Assistant .
When Xavier finally began developing Cerebro , he used Sage to beta test it , comparing the readings of the device to the readings achieved with Sage 's own mutant power .
In this timeline , Sage served as Xavier   's Executive Assistant .
When Xavier finally began developing Cerebro , he used Sage to beta test it , comparing the readings of the device to the readings achieved with Sage 's own mutant power .