There are several hypotheses about the origin of the dollar sign. It is first attested in American, Canadian, Mexican, Spanish American, and other British business correspondence in the 1770s referring to the Spanish American peso, also known as "Spanish dollar" or "piece of eight" in America, which provided the model for the currency that the United States adopted in 1792 and the larger coins of the new Spanish American republics, such as the Mexican peso, Peruvian real, and Bolivian sol coins. This explanation holds that the sign grew out of the Spanish and Spanish American scribal abbreviation "pˢ" for pesos. A study of late eighteenth- and early nineteenth-century manuscripts shows that the "s" gradually came to be written over the "p", developing into a close equivalent to the "$" mark. A variation of this hypothesis derives the sign from a combination of the Greek character "psi" (ψ) and "S".