Jon,
I agree w/Raul. The DB protractor is similar in design to the one Nottingham provides.
Raul, a quick of the Spacedeck is that the armpod swings in an arc towards/away from the table when a bolt is loosened. This has to be adjusted with the platter removed before you use any protractor. Until the pivot to spindle distance is in range, you can't stand a chance of getting close to correct w/a protractor. Cheers,
Spencer