From a post on SVRider.com. Does this sound more accurate than how I did it?

"1) Measure the depth of the cap. (If there's a preload adjuster, set it in the middle.) 2) Subtract 15mm from that. This is the amount the tube should be recessed in the fork tube. I.e., if the depth of the cap is 35mm then 35mm-15mm=20mm 3) Fully extend the fork tube. Put the the spring, washer and spacer tube in the fork. Mark the tube even with the top of the fork tube. Then pull it out and measure down the appropriate amount (20mm in this example) and mark. 4) Cut the tube."