I tried to use xrandr to set 1680x1050 as a new mode to VGA output, but it says:
sudo xrandr --addmode VGA-0 1680
X Error of failed request: BadMatch (invalid parameter attributes)
Major opcode of failed request: 140 (RANDR)
Minor opcode of failed request: 18 (RRAddOutputMode)
Serial number of failed request: 35
Current serial number in output stream: 36