I have often argued that the most common rocker radii measuring tool has measurement errors, because it only look at 3 very small points, and because it doesn't measure down the blade center or along the edges, but is offset in such a way as to be sensitive to nicks and scratches along the sides. (E.g., it may not measure the same radii along both sides.)
I believe you can get a better measurement by comparing the edges against a visual template.
If you want to measure your blade rocker, download and print this image of rocker curve templates:
http://mgrunes.com/boots/rocker.png
To print, scale and use the image, see the Rocker Template section of this page.
http://mgrunes.com/boots/BootBlade.html
Good luck.
Did anyone find this useful, or run into problems applying it?