From what I've seen, different calculators use different values. The KB calculator instructs you to add 15* to the 0.050" figure given on the cam timing card, I think to get you from 0.050" to 0.006". They're figuring that there is generally about 30* difference between the 0.050" closing figure and the 0.006" closing figure, 15* on the opening ramp and 15* on the closing ramp.