Apparent sidewall angles (SWA) were extracted from the measured profiles [Fig. 9(a), tip moving leftward] and were calculated using offline analysis software. The middle band of the sidewall (from 25% to 75% of the feature height) was determined for each edge and then the sidewall slope was determined from a linear fit to this segment of the edge. These results were averaged for all of the left and right edges in each scan line, and then averaged over all of the scan lines in each image. Table 1 shows the results of this SWA analysis for the J-tip scan shown in Fig. 9(a). The right edges of the features, which are in contact the end of tip foot, exhibit a larger apparent SWA than the left edges which contact the tip on the opposite side of the foot. Table 2 shows the apparent SWA extracted from a profile of the same grating imaged using an I-tip. The observed standard deviation of the SWA is relatively larger for the J-tip than for the I-tip, which means that the measurements using the J-tip were less stable. In contrast, the results obtained using the I-tip show symmetric SWA in the measured profile as well as better stability.