1. Opitz, C. J. An Ethnographic Study of Traditional Money;First Impressions Printing, Inc.:Ocala, FL,2000; pp92−97.
2. Ridgeway, W. The Origin of Metallic Currency and Weight Standards;Cambridge University Press:Boston, MA,1892; pp28−29.
3. M. Benvenuto purchased the authentic piece from a numismatics shop in Mannheim, West Germany when stationed there as a lieutenant in the United States Army in the mid-1980s. It has been in his personal collection since then.
4. Chemical Compositions of Chinese Coins of Emperor Ch'ien Lung (Qian Long) and Annamese Coins of Emperor Thanh Thai via Energy-Dispersive X-ray Fluorescence