-Your monitor has a well-defined and, under normal circumstances, unalterable size.
-Your monitor gets its information from your video/graphics card.
-Your graphics card is working with your operating system, and in your operating system you set your monitor to display a certain number of pixels horizontally and vertically. What this does is chop up your display like a mosaic, and every single unit of this mosaic is called a pixel. So, because your monitor has a fixed size, the size of each pixel is also fixed by the setting you choose in your OS. If, for example, you choose 640x480 on a 21inch monitor, you will see the pixels. On a 14inch monitor less, because on the 21inch (7-14-21) the pixels are one and a half times as large.
-In comes Photoshop. Self-assured, a tad pretentious even, but it cannot change the settings of your monitor as these are controlled from a layer below it, the layer of your OS.
- Let's assume you have your 17inch monitor set at its ideal resolution: 1024x768pixels. Even at full-screen, your monitor cannot display an image that is 2056 pixels wide. Whitch is why Photoshop has this button "Fit to screen". What this does is NOT change the size of the pixels (this is locked) but it only displays a part of them, in this case: half. The "Actual pixels" button displays the image at full size. It is important to grasp that "Fit to screen" does not change anything to your image, but only displays less pixels than are in your file. "Actual pixels" displays them all.
-And then comes the problem: print size... Best is to forget about this option, most v-certainly when you're on a PC. It gives, at the best an approximation. Win puters are default set to have 92 pixels in each inch, whilst Photoshop only calculates with 72. This is not contradictory to what I said above as it is mostly a calculating algorythm. And secondly: as seen, you can set youir monitor's pixels at whatever size you want. Conclusion: you will not see on your monitor the exact size of what you are going to print.
Final conclusion: see the "actual pixles" button as yet another shortcut for 100% zoom. Forget about the other two: it is better to see your image at 50% or 25% zoom as you get half/ one quarter of the pixels, and this you can better do with the Navigator pallette as "Fit on screen" does a bit what it pleases; and print size is completely unpredicrable.
