Measuring seat post length

Alibran

Just a quick question.

When measuring the length of a seatpost, where is the top point?

For example, on this seat post:
http://www.wiggle.co.uk/fsa-sl-280-seat-post/
do you measure to the join where the straight part of the post joins the head, or to the fixings that hold the saddle rails?

Thanks

cooldad

Generally the shaft length, but does it really matter? If the measurement is that marginal get a longer post.

Alibran

Thanks for the answer.

I asked the question because I needed to know the length of my current seatpost before I know what length I need.