Tweco 400 TS Arcmaster - Manual (Page 54)

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d) Turning the VRD ON/OFF. (see Figure 13)
To turn VRD ON: rotate the trim potentiometer (VR1) on the display PCB fully clockwise.
When VRD is turned ON check that it operates as per VRD Specifications on page 45.
To turn VRD OFF: rotate the trim potentiometer (VR1) on the display PCB fully counter-clockwise.
WARNING 9
The VRD ON/OFF trim potentiometer MUST ONLY be positioned fully clockwise OR fully
counter-clockwise as the VRD function will be unknown for every other position.
Figure 13. VRD ON/OFF Step D