I'm close to have finished the shed in which Im about to install a darkroom and Im planing the next moves (Building tables for enlarges, countes and storage etc). I figured I will Calibrate my two enlarger with dichroic heads (Omega D3 and Durst AC707) as in "Way Beyond Monochrome". So Im in need of some stepwedges, right? Stouffer has some: T3110; TP12-31 and TP4X5-31. Question is which to get and do I need 31 steps or will 21 do?