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A semiautomated measuring system is described which allows precise multiple measurements on organisms of biological interest. It consists of a microscope with drawing tube positioned next to a digitizing tablet which is interfaced to a personal computer; a TV camera and monitor are optional additions. Light from an LED fitted cursor on the digitizing pad is focused through the drawing tube and combined with the microscope image. Measurement signals are sent to the computer when the cursor button is depressed. Data storage, calculation, and display can be performed on-line as data are entered. Maximum precision of repeated measurements is ±0.04%; in routine use an accuracy of < ±0.25% is achieved. An example of its precision compared with a conventional eyepiece micrometer is given. The system has been used for measurement of a diversity of aquatic particles including phytoplankton, Zooplankton, fecal pellets, and stream benthic invertebrates at magnifications from 10 to 1250 power.
Roff et al. (Wed,) studied this question.