My MW posted an article about the "purple line" being used as a low tech, no risk way to follow a laboring moms progression and I found it really interesting so I thought I'd share!
http://www.scienceandsensibility.org/?p=5547&cpage=1

Also here was another great blog post that mentions it (along with other great ways to "measure" labor progression).
http://sarahvine.wordpress.com/2010/03/07/how-dilated-am-i-assessing-dilation-without-an-internal-exam/

And for *personal* experience, when I was relaying the info to DH he immediately cut me off & said "OH YEA, you totally had that! It was purplish-red". Kinda neat!