Dell 3115cn Color Laser Printer User Manual page 259

To specify the reference voltage settings for the transfer roller.
Values:
Plain -3 - +3
0*
Plain Thick -3 - +3
0*
Transparency -3 - +3
0*
Covers -3 - +3
0*
Covers Thick -3 - +3
0*
Label -3 - +3
0*
Coated -3 - +3
0*
Coated Thick -3 - +3
0*
Envelope -3 - +3
0*