[Lazarus] DateDif function needed

[Reimar Grabowski]

On Thu, 14 Nov 2013 07:19:56 +0100
Jürgen Hestermann <juergen.hestermann at gmx.de> wrote:

> Am 2013-11-13 19:42, schrieb Reimar Grabowski:
>  > 1 julian year = 365.25 days of 86400 SI seconds each.
>  > Of course there are lots of other definitions for year but if FPC uses the julian one the value is exact and no approximation
> 
> 
> So the difference between 2007-01-01 12:00 and 2008-01-01 12:00 ist *not* one year?
It is not one julian year. There is nothing like a year. As i said there are different definitions. If you talk about calendar year it's length changes and is therefor not a good measure of time and not used in science.

> It's only 365,00 days and therefore not a full year according to your definition.
Correct. And this is not my definition it is the correct definition of a julian year and it is based on SI units. Time is measured in SI seconds. If you cannot express 'your year' as seconds it is not a unit of time.

> But this it totaly wrong.
Care to elaborate? Or is it just your gut feeling?

> Same day same time of one year and the next should always be a one year difference.
According to what definition of year? Calendar year is a rather poor unit to measure time differences as it is not constant and cannot be expressed in seconds.

R.