The correct answer is B) comparing observed azimuths at different altitudes with computed values at the times of observation to see if the difference is constant. This is the correct answer because the accuracy of an azimuth circle can be checked by comparing the observed azimuths at different altitudes with the computed values at the times of observation. If the difference between the observed and computed azimuths is constant, it indicates that the azimuth circle is accurate and properly aligned. The other options are incorrect because they do not directly test the accuracy of the azimuth circle. Option A checks the accuracy of a terrestrial range, option C checks the alignment of the inner face markings, and option D checks the alignment of the relative bearing markings, but none of these directly test the accuracy of the azimuth circle itself.