The practical unit of resistance. The resistance of a column of mercury
one square millimeter in cross-sectional area and 106 centimetres long
at 0º C. (32º F.) The ohm used previously to 1884 is the B. A. Unit of
Resistance, q. v.

One legal ohm = 1.0112 B. A. Units, and I B. A. Unit = 0.9889 legal ohm.

The resistance of a copper wire 1 foot long and 1/1000 inch in diameter
is about 10 ohms. The resistance of 1 mile of iron wire 1/3 inch in
diameter is about 10 ohms.

Synonym–Congress Ohm.