Barnard, F.A. P., The Casting-Counter and the Counting-Board, Oxford: Oxford University Press, 1916.
Hudson, J.P., “Brass Casting Counters (or Jettons) Found at Jamestown,” Quarterly Journal of the Archeological Society of Virginia, 34 (1979), pp. 112-113.
Kidwell, P.A., A. Ackerberg-Hastings, and D. L. Roberts, Tools of American Mathematics Teaching, Baltimore: Johns Hopkins University Press, 2008, pp. 87-104.
Mitchiner, M., Jetons, Medalets & Tokens, The Medieval Period and Nuremberg, 1,1988, London: Seaby.
Pullan, J. M., The History of the Abacus, New York: Praeger, 1970.
Needham, J. with W. Ling, Science and Civilization in China, 3, Cambridge: Cambridge University Press, 1959.
Spasskii, I. G., “Proiskhozhdenie I istoriia russkikh schetov,” Istoriko-mathematicheskie issledovaniia, 5, 1965, pp. 269-420.
These objects, abaci in other Smithsonian collections, and related documents may be found by searching https://collections.si.edu/search/ for abacus.