Connecting a new monitor to my notebook results to 1024x768 only.
xrandr -q show only these possible modes

<code>
xrandr -q
Screen 0: minimum 320 x 200, current 2074 x 1400, maximum 8192 x 8192
LVDS1 connected 1024x768+768+0 (normal left inverted right x axis y axis) 246mm x 185mm
   1024x768      50.00*+  60.00    40.00  
   800x600       60.32    56.25  
   640x480       60.00    59.94  
VGA1 connected 1024x768+0+0 left (normal left inverted right x axis y axis) 0mm x 0mm
   1024x768      60.00  
   800x600       60.32    56.25  
   848x480       60.00  
   640x480       59.94  
</code>

So we need manualy add new mode (higher resolution)

<code>
   gtf 1400 1050 59.9
 
  # 1400x1050 @ 59.90 Hz (GTF) hsync: 65.11 kHz; pclk: 122.41 MHz
  Modeline "1400x1050_59.90"  122.41  1400 1488 1640 1880  1050 1051 1054 1087  -HSync +Vsync

  
</code>

<code>
   cvt gtf 1400 1050 60
# 1400x1050 59.98 Hz (CVT 1.47M3) hsync: 65.32 kHz; pclk: 121.75 MHz
Modeline "1400x1050_60.00"  121.75  1400 1488 1632 1864  1050 1053 1057 1089 -hsync +vsync
</code>

We simply add the generated line with better description  then "1400x1050_60.blabla" ex. "Lovely" mode

<code>
xrandr --newmode "Lovely"   122.41  1400 1488 1640 1880  1050 1051 1054 1087  -HSync +Vsync
xrandr --addmode VGA1 "Lovely"
</code>

Now we can easily select Lovely mode.