Filament Buddy. The helpful filament feed rate measuring tool.

So, you've been printing for a while with your shiny 3d printer, and you start to think to yourself, "I wonder if I can make this work better." A few Google searches later, and you've found yourself all sorts of guides and helpful tools like DaveD's profileinator http://www.thingiverse.com/thing:5310 . Woe be unto you, they all ask you to measure the filament pulled in over time. How on earth are you supposed to measure that curvy, unwieldy filament properly?

Well! Fret no more! The filament buddy is here to help! Simply mark the filament all the way around with a permanent marker then start extruding, when you see the filament hit the top of the patented (US Imaginary Patent Office: #31337) centimeter long "extrusion measurement reference window", hit start on your timing device. When it hits the bottom, hit stop. There you go! One metric cm of extrusion measured precisely over time.

http://davedurant.wordpress.com/2010/10/18/configuring-skeinforge-the-4-or-5-big-settings/