Ramps and dvr8825 (china), can't get vref value.

Ramps and dvr8825 (china), can’t get vref value.
I try to find the spot to read current voltage on vref on dvr8825 but can’t find where. Have read this: http://reprap.org/wiki/A4988_vs_DRV8825_Chinese_Stepper_Driver_Boards
But I get no reading. The slot; via gives 12.4 v, but must find where to read vref to change volt limit for stepper motor.

Measure on the ground pin and pot.