Since many of the documents I view and create on my computer claim to be based on real-world sizes (drawings in inches or mm, text in points, etc.), I’ve decided to finally calibrate my computer’s monitor, using the built-in Windows display control panel features.

For my CRT, with its current settings, the correct value turns out to be 85% of normal size—82dpi. I determined the value by holding a tape measure up to the screen, and adjusting the value until the on-screen scale matched the real one.

This feature has existed in Windows as far back as I can recall (at least back to Win98, and probably Win95), but its existance is little known, and rarely used correctly by applications. My use of it will allow me to test any application that has a “show actual size” feature. I’m not expecting it to be pretty, but it is the only way you should ever expect such a feature to display your work in its “actual size”.

There are many problems with its implementation, all the way through Windows XP:

• The on-screen ruler is too short to be entirely accurate. It should extend the entire length of the screen, to ensure the correct value can be entered.
• Windows only allows you to set this value globally, even if you need a different value for each monitor.
• The Custom DPI Setting is also burried where few people will ever find it. You must open the Display Properties control pannel, select the Settings tab, press the Advanced button, choose the Custom Setting… from the DPI Setting drop-down listbox, and then have a ruler handy with which to compare the on-screen ruler agains.
• Although you can adjust the calibration using either the percentage drop-down listbox or by dragging the ruler, you can do so only in whole percentage steps—which is usually more than one pixel—so the result might not be as accurate as it should be.
• Many of Windows’ built-in display items, including system fonts and icons, are pixel-based and don’t scale well when you choose a DPI setting other than the built-in ones, which are rarely accurate.

So far, the problems I have found that appear to result from using the correct value include:

• Windows scaling of some icons and text (the icons in the quick launch bar and the task bar) to the point of being distorted, when they shouldn’t be scaled at all, since they are designed in pixels.
• Some text and hyperlinks in the Mozilla browser being cut-off incorrectly at the top, bottom, or in the middle.
• A similar problem with images, with multiple white horizontal lines tarnishing some images, some of the time. In either case, highlighting and un-highlighting the text or graphics displays them properly, until you scroll the page. I’ve not seen this problem in Internet Explorer yet, just Mozilla.