Abstract
SUMMARY: Two devices for measuring the beam current in an electron microscope are described; a Faraday cage rod for accurate absolute measurements in the specimen position and a collector plate mounted in the viewing chamber, which may be used continuously during experiments, for relative current measurements. Results of experiments to determine the effect of secondary electrons on, and choice of material of, the collector plate are presented. An example of the use of the collector plate as a photometer is given.

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