"David St. John's His Book" de David St. John 1762 - 1840 - 181832.5 cm x 20 cm: A Cyphering book for currency conversions between the original United States 1818.

David St. John. A cyphering book (1818) kept by Revolutionary War soldier and veteran, David St. John (08/15/1762 - 06/06/1840) for calculating the differences between sterling money and the current lawful monies in circulation in the various states of America. A manuscript book of 125 pages, ink on paper. Signed on page 1 and elsewhere in the book, "David St. John[']s, his Book." Pages 1 – 29 are paginated by the author, pages 30 – 122 are not. Pages 123 – 125 are blank, but on the verso of page 125 there is an inverse notation in St. John's hand, which is dated 1818. Pages measure 32.5 cm x 20 cm. Stitched into a heavier paper wrapper with lap-edges, now worn with a horizontal tear on the back cover but still holding. Both covers were used as blotters. There is a patterned acid paper burn on pages 118-123, not affecting strength of the laid paper or its readability.

A manuscript text book for mathematics, starting with the four basic arithmetic functions: addition (simple and compound), multiplication and division) . The first cases illustrate subtraction, multiplication and division of "Federal Money."

Compound addition begins with "Sterling Money": "the money of account in great britain [sic] this has hitherto been the currency of the united states [sic] yet the value had depreciated in some states more [than] others although it was nominally the same throughout the pound is the money unit or integer." Application of compound addition to troy weight, avoirdupois and apothecaries weights follow. Cloth, dry, liquid (pints, quarts, gallons, hogsheads, pipes and tons) follow, as does long measure (barley corns, inches, feet, yards, rods, furlongs, miles and degrees). Land or square measure, solid or cubic measure and time are also included. Compound subtraction follows the same pattern and order, starting with "sterling money."

The most important record of reducing the currencies of the various states is in the "Cases" or rules to be followed which illustrate how a banker or businessman from a neighboring state calculated an equivalent currency value in the early decades of the American Republic. For example, Mr. St. John writes on page [57]: "To reduce new york [sic] and north [sic] Carolina currency to new england [sic] and virginia [sic] currency Rule Subtract a fourth." Many examples are given to "Fellowship" (Shares), Rule of Three, Rule of Three Inverse, Tare and Trett, Interest, Discount, Equation of Pay, Barter, Loss & Gain, Double Rule of Three, Alligation Medial, Promissory Notes and Tables of Even Parts.

David St. John enlisted on March 1, 1779 as a Private in Captain Jebez Gregory's Connecticut State Troops or Coast Guard and served in active service 1779 - 1781 under Col. John Mead and Col. Stephen St John and "was in the battle when Fairfield and Norwalk was burnt." St. John was also engaged in guarding the seacoast at Norwalk. See: Revolutionary War Pension and Bounty Land Warrant Application File W. 25,104, for David St John, Connecticut.