An ammeter is a device for measuring electric current. The analog ammeter is constructed so as to pass only a small (but known) fraction of the current to be measured through the meter movement that deflects the needle. This allows a very sensitive measuring device to safely measure large currents. The basic mechanism was developed by Edward Weston in the last few years of the 19th century. Analog ammeters have been almost entirely replaced in the last two decades by digital current meters.
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“Ammeter,” Digital Exhibits at Washington and Lee University Library, accessed September 20, 2017, http://omeka.wlu.edu/items/show/171.