Calculating field of view

Hello all and Happy New year!
Anybody got an idea how to calculate the field of view of any given eyepiece?
It seemed straight forward, but I got a little bit mixed up when they (new book I bought) started talking about "aparent field of view" and "True field of view"

Here's an eyepiece spreadsheet myself and Michael Scully prepared some time ago.
www.geocities.com/shannonsideac/epc.xls
Basically, if you know the focal length of the scope and the eyepiece, you can time the transit of a star (assuming you've tracking turned off). From this you can get the True and Apparent FOV.
Basically, Apparent Field Of View is what you see if you put the eyepiece up to your eye in a bright room, without actually putting it into the scope. Typically, each eye can see about 120 degrees (very rough figure plucked from thin air! ). Try putting an eyepiece up to your eye and you'll see roughly 50 to 60 degrees.
True FOV is what you see if you put the eyepiece in a scope. Basially, divide the Apparent FOV by the magnification and you'll get True FOV.
Hope this helps.

you can time the transit of a star (assuming you've tracking turned off)

I was afraid it was something like that- I was hoping there was a 'cleaner' method of calculation- oh well it's more fun to do it yourself I suppose

On another note- I finally got a clear night over Christmas where I could align the ETX scope correctly- took a while to figure out that the daylight savings time was set to 'on' :!:
Got some lovely views of Saturn, and just as it was slewing towards Andromeda the clouds started coming in. By this stage I was COLD and it was 3am.