find closest date (number) in a range

in short:
I have a variable, holding a date
What I hope to do, is search for the closest match to that variable in a range with different dates, stored in range a:a.
(when found, I want to select that cell. )


variable might for example be: 21.06.09 12:13

...............A
1 18.02.09 12:34
2 20.04.09 23:59
3 22.06.09 13:00
4 22.06.09 14:30

then here it should select cell A3 since this is the closest value.

any suggestions on how to achieve this?
I've searched a bit, but can only find examples for sheet-formulas to achieve this.

I assume I have to search for the numerical value of the date(s) in the range, compare them to my variable but alas, I have no idea how to do that :-/