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I'm trying to modify the screen resolution for my monitor in XFCE by modifying the file ~/.config/xfce4/xfconf/xfce-perchannel-xml/displays.xml

Here is the snippet I want to modify:

<property name="VGA-1" type="string" value="ACI 24&quot;">
  <property name="Active" type="bool" value="true"/>
  <property name="Resolution" type="string" value="1024x768"/>
  <property name="RefreshRate" type="double" value="60.003840"/>
  <property name="Rotation" type="int" value="0"/>
  <property name="Reflection" type="string" value="0"/>
  <property name="Primary" type="bool" value="false"/>
  <property name="Position" type="empty">
    <property name="X" type="int" value="0"/>
    <property name="Y" type="int" value="0"/>

I want to change the resolution to 1280x1024 with a refresh rate of 75 Hz. I'm inclined to make this change:

  <property name="Resolution" type="string" value="1280x1024"/>
  <property name="RefreshRate" type="double" value="75.003840"/>

I'm just curious about the new RefreshRate. I'm not sure why the current refresh rate of 60 Hz is specified as 60.003840 instead of just 60.0.

How was the decimal value for 60 Hz computed?
What should the value be for 75 Hz?

Also, is there an easier way to do this rather than modifying this file manually?

share|improve this question
If my math logic serves me right and assuming a few other things then you could use this formula for calculating 75Hz ((60.003840 / 60) * 75) – MonkeyZeus May 20 '14 at 17:35
60 Hz is just an approximation, since NTSC was adopted the signal for analog televisions has always been more/less than 60 Hz. It tends to work out to 59.94 (29.97x2), which is rounded up to 60 Hz. It does not much matter for LCDs, they can use any arbitrary timing the manufacturer wants, but that is the historical basis for 60 Hz not actually being 60 Hz. – Andon M. Coleman May 21 '14 at 21:01
60 Hz by itself is awful, it cannot be precisely measured in terms of ms-per frame. 16.666666667 ms is not a particularly useful interval of time in many applications that are scheduled in 1/5/10 ms increments. – Andon M. Coleman May 21 '14 at 21:10

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