or 



MATHEMATICS OF PHYSICAL PROPERTIES OF CRYSTALS 17 



COS U2 = COS ^ or ^''2 = zL 6 



tan f/'i = cot lA (5.10) 



tan Us = cot<t> 



Ui = yp -90 + nir 



U2= e 



Uz = <t> -90 + nir 



Fig. 39 — Cutting the slab and trimming it to the piezoid boundaries. 



