In a previous post, I discussed the benefits of taking apart used reeds and measuring the blades. You can read about it here
What I didn't describe in the old post, was how to measure the blade. You can use a dial indicator to measure, but keep a few things in mind. Since the tip of the indicator is rounded, it's best to measure the gouged side of the blade, not the exterior. This is because the rounded tip will conform better to the curve of the gouge, especially in the back of the blade where the curve is greater.
To make the blade as flat as possible without cracking it, you'll need to soak the cane. If you're in a hurry, you can boil it. Flatten the blade out using a heavy object like a paperweight and apply some downward pressure. Even if you get a small crack or two, you can work around this. You could also chop off the tube to eliminate cracking.
Measure the blade at each 1/8" from tip to collar. Measurement must be as accurate as possible so the numbers you get will accurately reflect blade thickness at all points. Mark the spine first by finding the exact midpoint of the width of the tip and the midpoint of the width at the throat. Connect the centers with a line. Do the same for the channels and rails.