Center of bottom-bracket to top of seat-tube is typical these days. One thing to be aware with Trek is that they give many of their frames not one, but two sizes. There is the measured size, and a so-called virtual size. Here's an old thread on how that works:

http://www.bikeforums.net/mountain-b...rtual-wth.html

I'm not sure the 3700 ever got the virtual-sizing treatment, but many of their mountain bikes have it. For that reason, I'm never really sure of what anyone tells me about their frame size on a Trek until I see the bike in person. I won't shop Trek on eBay for example, like I do other brands.