Well after almost a year of having a speedometer that read 20 when I was going 60ish I decided to get this thing calibrated. It started with pulling my head out of my ***, and actually thinking about what I was doing. Low and behold, it worked. They give you the chart of ratios in the instructions, as well as the ratio (that page was missing in my instructions, so I downloaded a new book) to figure out which one you need to get your speed close. After you get the speedo close, you adjust it with the up/down buttons to nail it. A little tip for tose of you looking for a place to start:

FYI, I have a 94 T-56 and a 3.27 rear.

Follow the directions for Application #3 except:

Set switch #4 to ON

Set the coarse calibration to 6
Set the fine calibration to 3.

That #4 switch was the sticking point, even the guy at Dakota Digital said it should definetly be OFF. After reading their chart (if you have their formula it makes a lot of sense) I figured that I'd try turning it on since that was the only way I could get the ratio high enough, and viola, it worked like a champ. The best thing is, once you figure out how to tweak this thing gear changes, tire changes are no longer a worry since you have infinate adjustability.