59.6 MB (6.1 MB compressed)
4236 x 4921 pixels
35.8 x 41.7 cm ⏐ 14.1 x 16.4 in (300dpi)
GEOFF TOMPKINSON / SCIENCE PHOTO LIBRARY GEOFF TOMPKINSON / SCIENCE PHOTO LIBRARY
Circuit testing. An engineer checks current flow through circuit boards at a telephone exchange. He is holding a voltmeter. Most modern exchanges use solid-state devices to carry out the switching process, with computers to control the operation.
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