This is a model of part of a helicoid with parametric equations x(t)=u.cos(t), y(t)=u.sin(t), and z(t) = 2t/3, where the parameter u goes between -1 and 1. The parameter t goes between 0 and Pi for the half-twist, goes between 0 and 2Pi for the full-twist. This model was designed and printed by my WLU summer research student Emily Jaekle ('16). See http://mathvis.academic.wlu.edu/2015/07/27/helicoids/.