Alvin 12" adjustable drafting triangle with computing trig-scales features 3 sets of graduations showing rise and slope from 0 to 90 degrees. Desired angle is locked into position with a thumbscrew for accurate drawing. Strong 0.120" thick acrylic plastic is shatterproof light blue, optically clear. Inking edges on all 3 sides. Available in 3 sizes as shown. Detailed instructions included. Alvin LX712K adjustable drawing triangle.