To facilitate a more rapid and accurate method of assessing and analyzing aerosol droplets deposited on glass slides, a one-hand-operated caliper-type measuring device equipped with an automatic data-collection system was developed. Having received a signal from the caliper indidating the measurement of a discrete particle, the automatic data-collection system will record the information on punched paper tape in a form directly acceptable by those electronic computers that accept binary-coded decimal paper tape as input. Using the device described, it is possible for one man to measure and record simultaneously on paper tape an average of 60 drops per minute (the maximum being about 180), reducing the man hours per thousand drops to about 0.28. (Author).