Screen Ruler Pro / Help

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"Calibration" means setting the proper PPI values for any display attached to your computer.

  • PPI (pixels per inch) is the actual number of pixels in one inch
  • PPI - X is the number of pixels per inch on the horizontal (X-axis)
  • PPI - Y defines the number of pixels per inch vertically (Y-axis)

To calibrate your screens, open the Preferences window and go to the displays tab.

Click Detect Displays (you will need to do that if you attach new display to your computer too).

In the table in the left side you'll see all system displays with their respective PPI (pixels per inch) resolution for the X and Y axis respectively. By default Mac OS will put 72ppi while Windows will return 96ppi. In both cases, the default value will most probably be wrong. Every screen comes with many different characteristics (resolution, width, height, diagonal) and the only way to find the real PPI resolution is by using the PPI Calculator (right under Detect Displays button).

To calculate the PPI value:

  • click on the screen you are calibrating in the list;
  • check the width and height values in the calculator;
  • enter the diagonal of your display (Be sure you enter the right value here. Some manifacturers may give rounded diagonal for their displays -- for example my display is labeled as 20 in but it's actual diagonal is 20.1 in)
  • click Enter to calculate the PPI (this will enable the "Set to Display" button below)
  • click the Set to Dixplay button to apply the new PPI value

Note: The PPI Calculator presumes square pixels. (If you don't want what that means, don't worry. I am 99.99% sure your display comes with square pixels so you may stop reading now.)

Square and rectangular pixels:

On most displays (I believe that's true for almost any modern computer screen) the PPI-X and PPI-Y values are the same (i.e. "square pixels"). However, if your device or operating system resolution uses non-square pixels, you can fine-tune the respective PPI value for the X or Y axis.

You may need to set different PPI - X and PPI - Y values only if the actual size (in inches, centimeters etc.) of one unit (1 inch, for example) is different when you measure horizontally and vertically.



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