SLIDESHOW : Pencil Measuring
Here’s a great set of graphics that shows how to do a classic art technique. You can measure and transfer proportions when drawing a live subject. Artists have been using this one-eye-closed method for years, to find two measurements that correspond in some way. First, you find one measurement. Then, while holding a pencil up at arm’s length for consistency, you find another that is either the same length, or a multiple of it. Once you get a proportion, you can it on at any size on your work for better accuracy.