A: There is no one correct FOV for this game. And frankly trying to play arma with a corrected or "perfect" FOV may turn out to be extrememly difficult or impossible without the proper hardware. ie Triple-head.
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Measure the height of your monitor's screen, top pixel to bottom pixel.
Now measure from your eye (normal playing position) to the top of the screen and then your eye to the bottom.
Something like this:
http://img.photobucket.com/albums/v504/F12Bwth2/Game%20Screens/FOV.pngPlug those number into this calculator like so.
EXAMPLE (using inches):
http://img.photobucket.com/albums/v504/F12Bwth2/Forums/FOVCalc.pngCALCULATOR: http://ostermiller.org/calc/triangle.htmlThat 17 degrees was my real life vertical FOV. I have since moved my monitor closer to me by 5 inches and now have a V-FOV of ~20.5 degrees.
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Adjusting the FOV in arma is a simple matter of editing your
"C:\Users\Username\Documents\ArmA 2\Username.ArmA2Profile"
Open it in notepad.
Search for "fov". There are only 2 lines that contain fov near the bottom. They are
fovTop=XXXX; (THESE NUMBERS ARE IN RADIANS!!!)
fovLeft=XXXX;
(my fov was blanked to prevent confusion)
BI (being Czech) has labeled them FOVTOP (Vertical FOV)
and FOVLEFT (Horizontal FOV) Also being Czech if you want to set your Vertical FOV to say.. 75 degrees you must type. 0.75. A value over 100 like 112 requires 1.12
You do not need to use the decimal places found in fov fields!! The game will take the second value and round it off to some obscure decimal you do not need to tell someone to set their fov to 84.2398439. Just say.. 84.
You only need concern yourself with finding the fovTop value. The fovLeft value is determined using your monitor's aspect ratio (ie 16:9, 16:10, 4:3) and a calculator.
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Setting my arma to my perfect V-FOV of 20 degrees with a 16:10 screen a means a horizontal value of 32.
That looked like this after using google to convert to radians.
fovTop=0.357;
fovLeft=0.572;
http://www.youtube.com/v/h3vnRIsHG-AIn that video you see 20, 40, 60 and 80 radians tested. Having only one screen makes using that perfect FOV difficult. It would be almost impossible to go through a town without looking around (via mouse look or TrackIR) constantly to see enemies.
I can vouch that it is a much more realistic play experience and would be even more if the ironsight zoom was disabled. Should you have a projector or large TV and sat close enough (not so close that you go blind!) you could set the fov to a calculated value closer to a playable number. Currently I have chosen 65x104.
fovTop=0.65;
fovLeft=1.04;
65 Radians is nowhere near my "perfect" V-Fov of 20° (0.35 radians) but until I have a 3 display system or use my XGA projector to play I have to live with it.
Feel free to experiment and post your thoughts here. If your interested here is the rFactor FOV tutorial discussing the same type of modifications.
http://www.racesimcentral.com/forum/showthread.php?5691-Setting-up-your-Driving-view 
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