A commonly cited proof in favor of the May 21st date is:
According to Camping, the number five equals "atonement", the number ten equals "completeness", and the number seventeen equals "heaven".
Christ is said to have hung on the cross on April 1, 33 AD. The time between April 1, 33 AD and April 1, 2011 is 1,978 years.
If 1,978 is multiplied by 365.2422 days (the number of days in a solar year, not to be confused with the lunar year), the result is 722,449.
The time between April 1 and May 21st is 51 days.
51 added to 722,449 is 722,500.
(5 x 10 x 17)2 or (atonement x completeness x heaven)2 also equals 722,500.