... However, to avoid excessive central obscuration, a conical baffle is necessary in addition to the usual primary and secondary baffles. ... At that time, it was complete except several outside ribs remained to be attached and the upper and lower edges needed to be chamferred. ... The cone was measured at four equally spaced locations very near its upper and lower edge (Table 3). ... A tape measure was used to measure four diameters of the baffle at its upper and lower edges (Table 4). ...