http://www.parallax.com/dl/docs/cols/nv/vol8/col/nv142.pdf
http://www.parallax.com/dl/docs/cols/nv/vol8/col/nv141.pdf
http://www.parallax.com/dl/docs/cols/nv/vol7/col/NV139.pdf
http://www.parallax.com/dl/docs/cols/nv/vol7/col/NV137.pdf
http://www.parallax.com/dl/docs/cols/nv/vol7/col/NV129.pdf
http://www.parallax.com/dl/docs/cols/nv/vol6/col/nv125.pdf
http://www.parallax.com/dl/docs/cols/nv/vol6/col/nv122.pdf
http://www.parallax.com/dl/docs/cols/nv/vol6/col/nv117.pdf
http://www.parallax.com/dl/docs/cols/nv/vol5/col/nv116.pdf