A traditional Scottish unit of volume equal to 2 mutchkins or 1/2 Scots pint. The choppin is equivalent to about 52.1 cubic inches, 1.80 U.S. liquid pints, 1.50 British Imperial pints, or 854 milliliters
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}