We have examined sources of error and techniques for error avoidance in Schottky barrier surface photovoltage measurements. In particular we have used a computer simulation approach to gauge the errors in the method A formalism, which is applied to analyzing constant open-circuit voltage measurements, and in the method B formalism, which is applied to analyzing constant light flux measurements. As a result of this analysis, we have shown we can eliminate the extreme measurement precautions necessitated by method B through the use of a new method C formalism which is introduced here. We also show that, for measured diffusion lengths less than one-third the sample thickness, the measurement is shown to be forgiving of the state of the back contact if that surface has flat or accumulated bands; however, if the back surface is rectifying, the range of the measurement validity can be affected by the magnitude of the front contact barrier height, even with the measured diffusion length less than one-third the sample thickness.