In a leap year (every forth year) the months have alternately 31 and 30 days giving a total of 366 days.
Thus, in non-leap years the last month February would have 29 days is place of its usual 30.
Add 621 to the date given in the Persian calendar and you'll get the Gregorian. The only difference is its starting point, which is the birth in 559 BC of Cyrus II, the Persian Empire founder, also known as Cyrus the Great.To convert, instead of adding 621, you'll have to subtract 559.It modified the Julian calendar in order to correct the accumulated errors of 11 minutes 10 seconds in each Julian year.10 days were removed in 1582 in those countries that adopted the Gregorian calendar.In the Julian calendar 24th March 1701 is followed by 25th March 1702!
So, someone born on 20th March 1701 and dying on 30th March 1702 is only 10 days old.
As a genealogist, any date you find in old records before 1752, and between January 1st and March 24th, inclusive, should be expressed as a double date.
The authors of the documents did not do it for you in most cases.
After 1752, the use of double dating was widespread in the old documents.
In order to calculate ages when the dates span 1752, use the second number in both cases and assume that pre 1752 years start on the 1st January.
For instance, year 2535 of the Imperial Persian calendar began at the Spring equinox in 2535 − 559, i.e. It ended the day before the Spring equinox of the following yer, i.e. Writing years is to be proceed the same way as in English. Moreover, Iranian people have a specific design for some figures (1st line) in comparison with the rest of the Arab world.