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Calculate the approximate number of years between two DateTime values.
Source position: dateutil.inc line 271
function YearSpan( 
const ANow: TDateTime; 
const AThen: TDateTime 
):Double; 
ANow 

First moment in time 
AThen 

Second moment in time 
Number (fractions included) of years between ANow and AThen
YearSpan returns the number of years between ANow and AThen, including any fractional parts of a year. This number is an approximation, based on an average number of days of 365.25 per year (average over 4 years).

Calculate the approximate number of months between two DateTime values. 


Calculate the approximate number of weeks between two DateTime values. 


Calculate the approximate number of days between two DateTime values. 


Calculate the approximate number of hours between two DateTime values. 


Calculate the approximate number of minutes between two DateTime values. 


Calculate the approximate number of seconds between two DateTime values. 


Calculate the approximate number of milliseconds between two DateTime values. 


Calculate the number of whole years between two DateTime values 
Program Example63; { This program demonstrates the YearSpan function } Uses SysUtils,DateUtils; Procedure Test(ANow,AThen : TDateTime); begin Write('Number of years between '); Write(DateToStr(AThen),' and ',DateToStr(ANow)); Writeln(' : ',YearSpan(ANow,AThen)); end; Var D1,D2 : TDateTime; Begin D1:=Today; D2:=Today364; Test(D1,D2); D2:=Today365; Test(D1,D2); D2:=Today366; Test(D1,D2); D2:=Today390; Test(D1,D2); D2:=Today368; Test(D1,D2); D2:=Today1000; Test(D1,D2); End.