This is explained in

` perldoc Date::Calc`
`* "($Dd,$Dh,$Dm,$Ds) = Delta_DHMS($year1,$month1,$day1,
$hour1,$min1,$sec1, $year2,$month2,$day2, $hour2,$min2,$sec2);"
This function returns the difference in days, hours, minutes and
seconds between the two given dates with times.
All four return values will be positive if the two dates are in
chronological order, i.e., if date #1 comes chronologically BEFORE
date #2, and negative (in all four return values!) if the order of t
+he
two dates is reversed.
This is so that the two functions ""Delta_DHMS()"" and
""Add_Delta_DHMS()"" (description see further below) are
complementary, i.e., mutually inverse:
Add_Delta_DHMS(@date1,@time1, Delta_DHMS(@date1,@time1, @date2,@ti
+me2))
yields ""(@date2,@time2)"" again, whereas
Add_Delta_DHMS(@date2,@time2,
map(-$_, Delta_DHMS(@date1,@time1, @date2,@time2)))
yields ""(@date1,@time1)"", and
Delta_DHMS(@date1,@time1, Add_Delta_DHMS(@date1,@time1, @delta))
yields ""@delta"" again.
The result is zero (in all four return values) if the two dates and
times are identical.
`

--Jim

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