Ball 1 : A unit measuring the degree of ice coverage of polar seas. One ball equals 10% coverage. The unit was invented by the Russian naval officer N. N. Zhubov (1895-1960)
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}