Bicycle Mechanics - Measuring spoke length

This may be a REALLY elementary question, but I am having some trouble finding an answer.
I took a broken (at the elbow) spoke to my LBS to get a replacement. They measured it and sold me a handfull of spokes. I didn't think to measure them it at the time and, I have used a couple as spokes have broken, including one this morning. I decided to go ahead and order a box to have on hand and went to measure a spoke to see what size to order. I grabbed the broken one (again, at the elbow) and one of the new ones, stood them on the threaded end and held a ruler up next to them. The new spoke seems to be about 4 mm longer than the broken on, measuring to the (approximate) inside of the elbox. Now I am 1) wondering what is the correct way to measure a spoke and 2) picturing 3-4 mm of spoke extending through a couple of nipples, threatening my tube!
So my question is, what is the correct method of measuring a spoke? Also, I have read that a spoke stretches under the tension of tightening. Is it necessary to adjust any actual measurement of a broken spoke to allow for this, ie, subtract 1-2 mm, or is the stretching so minimal as to be irrelevant?
Help, I am imagining a hissing sound already.
Thanks,
Raymond

DT's home page should cover the details of this and it has a spoke calc also.

http://www.dtswiss.com/

What LBS was it. I used to work at two of the shops in New Orleans. When ever I need something now, that I cant get myself, I go to Bayou Bicycles.

Hey, Mick! At last another New Orleanian. Bayou is my place though I got these spokes at Pauli's which I was passing when I remembered I needed some spares. I could just get some from Mark, but I was ordering some other stuff online and thought I'd just add a box of spokes to the order. I get just about everything from Bayou, including a lot of upgrade stuff lately that I could have gotten for a lot less online. But it was worth the extra money since they will install and do it correctly as opposed to my doing it, taking forever, and probably not getting it right. Send me an email at
RainmanP@att.net
We'll chat.
Regards,
Raymond

The DT calc is new and I haven't used it yet, but I seems good.

Here is a link to download the spoke calculator I use. Works well and has a good database of hubs and rims.

http://www.damonrinard.com/spocalc.htm

Rainman, measure your spokes from the inside of the shoulder, don't forget the spokes on the drive side of your rear wheel are aprox. 2mm shorter.

Steve33.