Excuse really late reply, house move fell through so I've been temporarily staying with family, no internet out in the sticks....
My Holbrook"s the C13, looks a lot like the C8 Electronic, scaled up a bit, the TTA has an calibrated adjuster and scales at each end of the guide (Sine?) bar, taper per foot one end, degrees/minutes the other, but I still like to check with a reference (e.g. a bought taper between centres) or a DTI/DI on the toolpost and the Trav-A-Dial