For a more accurate measurement of fork rake, I like to remove the fork and do kind of a home machinist thing. I clamp a bare front hub into the fork (a spare vintage Super Record of course!) and set it down on a level section of my kitchen counter. The Fat Max level (low cost, high accuracy) tells me what's actually level. I use books, tools, pads of paper or whatever to shim under the steer tube until it is level. With a digital or dial caliper (correctly zeroed) I measure the hub flange diameter, the distance from the bottom of the steer tube to the countertop, and the distance from the top of the steer tube to the countertop.
The difference between the bottom distance and the top distance is the height of the steer tube center above the countertop. The hub radius divided by two is the height of the hub center above the countertop.
The difference between the hub center height and the height of the steer tube center is ,,,, the fork offset!
If you've done everything carefully and read the level and caliper correctly, the accuracy of the answer should be within a 10th of a millimeter or 5/1000 of an inch. Pretty good for a kitchen counter!