Decimal Day and 10p coin equivalents, co-existed in circulation as valid currency until the early 1990s. In theory this included coins dating back to 1816; in practice the oldest were dated 1947, when these coins stopped containing silver. The coins were withdrawn when smaller 5p and 10p coins were introduced in 1990 and 1992 respectively. The face value of Maundy money coins was maintained, increasing all their face values by a factor of 2.4, as the coins continued to be legal tender as new pence. The numismatic value of each coin, though, greatly exceeds face value. The decimal halfpenny (p), introduced in
Cocker's Decimal Arithmetick Cocker's Decimal Arithmetick Cocker's Decimal Arithmetick is a grammar school mathematics textbook written by Edward Cocker (1631–1676) and published posthumously by John Hawkins in 1684. "Decimal Arithmetick" along with companion volume, "Cocker's Arithmetick" published in 1677, were used in schools in the United Kingdom for more than 150 years. The concept of decimal fractions and the advantages of using them in calculations were well known, but a wide variety of different notations were in use. After surveying various notations, "Decimal Arithmetick" recommends the decimal point notation introduced by John Napier: "Decimal Arithmetick" gives instructions for calculations involving decimals, methods of