The background: InDesign was unable to display work at true actual size until CS6 came along. (So that 1 inch on the screen rulers equals 1 inch on a physical ruler.) Unfortunately, CS6 still doesn't get it right if your display is set to something other than its native resolution. For example, if I set my 27" NEC SpectraView display to "Best for Display" in the Displays system preference panel, then viewing at "Actual Size" in Indesign CS6 achieves true actual size. But that resolution is way too high, making the features of the user interface way too small. The comfortable display resolution is "scaled" to 1920x1080, which provides a nice 2-page layout viewing area (at true actual size) plus a comfortable user interface. However, InDesign CS6 ignores this and continues to draw the "Actual Size" view based on "best for display" resolution, and that results in a greatly shrunken image. Acrobat Pro has gotten this right for several versions now, but it is apparent from this and other CS shortcomings that the different product groups at Adobe aren't very good at what Samsung does and fail to copy each other's work.
The solution to achieving "true actual size" is a script written by Dave Saunders (and probably others) some time ago:
//by Dave Saunders. Replace the percentage number with the correct value for your screen
app.layoutWindows.zoomPercentage = 113;
If you're like me and don't really use scripts, here is what to do with it on a Mac (with apologies to Dave and other experts who know a helluva lot more about this than I do):
1. Copy the text for the script and paste it into the blank window that opens when you start ExtendScript Toolkit CS6 (in Applications>Utilities>Adobe Utilities - CS6). Leave it open.
2. Go to Acrobat Pro>Preferences>Page Display and under Resolution note the number associated with "Use system setting". (On my system it is 81 pixels/inch.) I also suggest enabling that setting if it isn't, so that Acrobat also displays at true actual size.
3. Divide the number from Acrobat by 72, then multiply by 100. (This is essentially a percentage calculation of system resolution over the conversion value of 72 points/inch, which produces 112.5 in my example. I round it to 113.)
4. In the open script, change the number to what you got from the above result (113 in my example).
5. Save the script with a name such as "True actual size.jsx" and leave it on the Desktop where you can get it at later for dragging.
6. In InDesign, go to Window>Utilities>Scripts, then right click on User and choose Reveal in Finder. Drag your script into the User folder. (I recommend option-dragging it to leave the original on your Desktop for archiving.)
7. Test the script in an open InDesign document by double clicking on the script. The display should now show your work at true actual size.
8. The scripts window is awkward at best, so the last step is to assign a keyboard shortcut to your script. I use Control-1. Go to Edit>Keyboard Shortcuts… and choose Scripts. Scroll down to the bottom, where you should see your script listed. Highlight it and enter Control-1 (or whatever you prefer) into the New Shortcut window and click Assign. Then click Save. You won't be allowed to modify the Default set, but I was fine with "Default copy".
Now whenever you want to view your work at true actual size, just hit Control-1 (or whatever you chose for a keyboard shortcut).
You might want to copy these instructions into a TextEdit file and put it with your script file in a folder that you can find when the time comes to upgrade to CS7, because I'll lay odds that you're going to need to achieve true actual size all over again.
Lastly and far from least, thank you for the script, Dave! If you or other pros come across this and see corrections or improvements, please set me straight.