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CMTS was checked for confidence of position repeatability by moving the headpiece and then returning it to the same position (as indicated by the CMTS vernier dials) before each of 32 trials. The results corroborate the accuracy of the CMTS by showing a maximum standard deviation of position means increase of 0.04 mm beyond that found in the first test. The third test further investigated position data fluctuations due to drift over 25 trials. In this test the PSS was powered down for awhile after each of the first two groups of 5 trials and then the PSS was allowed to idle with power on for an hour after each of the second two groups of
5 trials. The results show a substantial increase in the standard deviations of the position means. The fourLt-h test examined the influence of acoustic source use on drift and involved transmitting 2000 clicks between each group of 5 trials for a total of 15 trials. The results of this test indicate that acoustic source usage does not exert a strong influence on drift.
The next series of tests characterizes the DAS for headpiece position data accuracy over a portion of the system's operational range with the use of the CMTS. Of interest is not only the accuracy of the absolute coordinate values but also the accuracy of changes in the coordinate values resulting from small positional perturbations (indicating relative position accuracy) over a range of nominal positions. The results of 5 tests are summarized as error means and standard deviations in Table 3. In each
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