These variables and the code inside the GetDatePart is used to calculate the proper year, day and month from ticks, taking into account the Leap Years:
So for example the num1 will give you the days since it is: ticks / this.TicksPerDay.
Then num2 will be used to keep how many of 400 years there are, to calculate further how many are the leap years, and co on. If you will rewrite the code, you don't actually need to keep this private variables.
GetDatePartDay is actually the reverse of the GetAbsoluteDate function. See the GetAbsoluteDate function, it is a bit more easier to understand. If the Persian calendar has different calculation of the leap years, you will need to rewrite both GetAbsoluteDate and GetDatePartDay functions.
On a side note, you said you bought the controls, but I don't see any license linked on your account, if you have any problems with your account and/or sending support tickets, you could contact to our sales department to figure out what is happened.
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