The non-reciprocal phase shifter in the design of the waveguide differential phase-shift circulator consists of two or four suitably magnetised ferrite tiles on the top and bottom walls of the waveguide. It may be adjusted in terms of a reciprocal condition and a non-reciprocal one. The first condition essentially fixes the geometry of a typical phase-shift section except for the thickness of each ferrite tile; the second determines the connection between the split-phase constants and the thickness of the tiles for parametric values of gyrotropy. The purpose here is to satisfy the first requirement of the two-tile geometry using a calculation and to meet the second one by having recourse to measurements. It includes some preliminary experimental data on new four- and eight-stacked ferrite tile structures. It is likely to prove of value in the design of large continuous wave power devices.