After Grahame’s excellent suggestion I did some testing.
The result was that...
6 pushes of the zoom button = 100% magnification (Setting, custom setting f1, to automatically zoom, to medium magnification, when you press the multi selector center button will give you the same zoom level.
Here is how I determined this...
100% zoom or crop is defined as --->> 1 pixel in the image = 1 pixel on the display.
The D300 LCD pixel dimensions are 640px x 480px (this is from the DPR D300 review--->> “922,000 pixels (VGA; 640 x 480 x 3 colors”)
I used Corel Draw to create a grid pattern on a sheet of paper.
I filled in 4 squares in the center of the grid as a reference to identify the center of the frame.
Then, I photographed the grid pattern with the focus point over the marked squares.
I copied the image to the computer and exported it as a TIFF file and then returned the card, with the original NEF, to the camera.
I then, created a blank Photoshop document to match the size, in pixeles, of the cameras LCD --> 640 pixels wide by 480 pixels high.
I opened the full size image (4288px x 2848px) of the grid.
Then, selected the entire grid image, copied and pasted it into the new blank document.
I centered the grid image in the blank document and flattened the layers. This gives me a 100% crop of the grid image at 640x480 pixels matching what you should see in the camera LCD at 100% zoom.
Then, I compared the Photoshop image to the actual image on the cameras LCD. At 6 pushes of the zoom button the visible image area image on the camera matched the 640x480px, 100%, crop in Photoshop.
Here are the images...
Full Frame for reference (size reduced for posting)
Comparison of Photoshop image and LCD image. (the 100% crop image has not been reszied for posting)