A [[resistivity]]-measuring system using a "normal" electrode configuration. A constant current is passed between a current [[electrode]] on the [[sonde]] ([[A electrode]]) and one at the surface ([[B electrode]]) while the potential difference is measured between another on the sonde ([[M electrode]]) and a reference electrode ([[N electrode]]). The "spacing" is the diference between the A and M electrodes. Usually spacing of about 16 inches is used for a the short normal and 64 inches for the medium or long normal. The [[measure point]] is midway between the A and M electrodes.

A normal device has a [[depth of investigation]] said to be about twice the [[AM spacing]]. The normal is an unfocused device which produces a symmetrical curve which has been particularly useful in [[correlation]] and indetermination of [[lithology]]. [[Formation]] detail can be increased by decreasing the AM spacing, but depth of investigation suffers.

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