Originally Posted by Mark Kelly

A much cheaper way than all the above.

Make two marks a suitable length apart on the bike and determine their distance with a tape measure; C to C top tube length is often convenient. Stand the bike against a wall as close to vertical as you can, stand well back (the further the better) and take a digital photograph at approximately top tube height.

Load the result into a program like Irfanview and use the crop box (which gives box dimensions in pixels) and the the fine rotation feature to determine the appropriate dimensions.

As an example, say your top tube is horizontal and your measured 565 mm C to C distance comes out at 795 pixels. You then know that each pixel is 565/795 = 0.71 mm. You find that you have to rotate right by 71.4 degrees to get the head tube vertical, so that's your head tube angle. Lining the edge of the crop box down the centre of the head tube on the rotated image, you expand it sideways until the other end bisects the front axle. The crop box width is given as 63 pixels. 63 x 0.71 = 45 mm so that's your fork rake.