Noun
A case or box placed near the helmsman, containing the compass of a ship, and a light to show it at night.
Source: Webster's dictionaryCompass correction main A binnacle containing a ship's standard compass, with the two iron balls which correct the effects of ferromagnetic materials. Source: Internet
The effect of ferromagnetic materials in the compass's environment can be corrected by two iron balls mounted on either side of the compass binnacle. Source: Internet