I use this one andit seems to be accurate. Now you need to read the foot note and make sure the numbers you are putting in are correct.
United Engine & Machine Co. Incorporated
Now if your numbers are at .050 then you need to add 15 degrees but if its at .006 then that number is pretty close and can be used. I do not know of anyway to convert to zero. Just keep in mind some cams have longer ramps then other so .006 can be longer on different cam types and mfr.
Dcr veries with head material and setup and how tight the squish is when complete.