Among the unique plasma diagnostic capabilities of a heavy ion beam probe (HIBP) system is the direct, local measurement of the electric space potential. To make this measurement, it is necessary to accurately determine the accelerator voltage (for the probing ion energy) and the energy of the secondary (+2) ions leaving the plasma, since the measured potential is the difference betweeen these two quantities. The Proca and Green electrostatic energy analyzer we use for the latter purpose, provides the required accuracy if we can demonstrate that the detected ions enter within a narrow angular window. One of the key issues being addressed during the initial operation phase of the MST HIBP is angular alignment. The process is made easier by the excellent reproducibility of MST discharges, but more difficult by our extensive use of cross-over sweep plates, which add to the complexity of the electric field experienced by the detected ions. Also, the apertures we have incorporated to protect the sweep systems from plasma and UV flux put bounds on the possible angles. Initial experimental results obtained in aligning and confirming calibration of the analyzer during MST discharges will be discussed, as will be features of detected potential signals.