Gnome Screen Ruler
Copyright (c) 2004 by Ian McIntosh

== Ruler Accuracy ==

There are two issues regarding ruler accuracy.

(1) All units except Pixel and Percentage rely on your computer's DPI setting.
If this number is set accurately, the ruler will be quite accurate (you can 
hold a real-world ruler up to your screen, and they will line up).  If this
number is not set accurately, the ruler will be completely inaccurate.

However, inaccurancy isn't all bad because something that looks like
3 inches next to an inaccurate screen ruler will still *print* as 3 inches.

(See far below for instruction on setting your screen DPI and some good DPI 
settings to use.)


(2) The screen ruler uses the CENTERS of pixels for measurements, when it
might be more accurate to use the EDGES of pixels.  Unfortunately, computers
don't deal well with pixel edges.  For example, the mouse cursor jumps from
pixel center to pixel center.

If we measured from the left edge of the first pixel to the mouse cursor, all
measurements would end in ".5".  This would be confusing, so we *round down*.
This could be thought of as measuring from the left edge of the ruler's first
pixel to the left edge of the pixel pointed at by the mouse cursor.


== DPI Settings ==

If you want the screen ruler to be accurate on-screen, set your DPI based on
your screen resolution and size.

(Don't know your screen resolution?  Find it under 
Desktop Preferences / Screen Resolution)

Resolution	Screen	DPI
----------  ------  ---
800x600		12"		83
800x600		14"		71
800x600		15"		67

1024x768	14"		91
1024x768	14.1"	91
1024x768	15"		85
1024x768	17"		75

1280x960	14"		114
1280x960	15"		107
1280x960	17"		94

1400x1050	14.1"	124
1400x1050	15"		117
1400x1050	16"		109

1600x1200	17"		118
1600x1200	19"		105
1600x1200	21"		95

If your setup isn't listed, calculate it as:
(screen horizontal resolution) / (screen size * 4/5)

Example for 15" @ 1024x768:  1024 / (15 * 4/5) = 85.33 (round to 85)

(All of this assumes your screen is a 4/3 ratio.  If yours isn't, just divide
your horizontal resolution by your screen's width in inches to get DPI.)

---

To change your DPI setting:

Run Font Preferences (Desktop Preferences / Font)
Click the "Details..." button.
DPI (dots per inch) setting is at the top.
