MLA

Playfair, William, 1759-1823. Chart shewing the value of the quarter of wheat in shillings & in days wages of a good mechanic from 1565 to 1821. Undated. https://collections.library.yale.edu/catalog/2066758.

APA, 6th edition

Playfair, William, 1759-1823. (Undated)[Chart shewing the value of the quarter of wheat in shillings & in days wages of a good mechanic from 1565 to 1821]. https://collections.library.yale.edu/catalog/2066758.