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easiest to distinguish. Taking into account the particle image size as projected on the tablet, the estimated human error in particle center location was less than one-third of the radius of a particle or + 0.01 mm in true position in the test pipe. Both m a c h in e and human errors could be reduced to less than one-third by using the now available 0.914 by 1.219 m tablet and enlarging the frame to fit the larger tablet which has the same + 0.127 mm resolution associated with it.