Penny (Irish decimal coin) Penny (Irish decimal coin) The decimal one penny (1p) () coin was the second smallest denomination of the Irish pound. It was first issued when the Irish currency was decimalised on Decimal Day, 15 February 1971. It was the second of three new designs introduced all in bronze, the others being a half-penny and a two pence coin. All featured ornamental birds designed by Irish artist Gabriel Hayes on the reverse. The coin originally had a diameter of 2.032 centimetres and mass of 3.564 grams consisting of copper, tin and zinc. This was identical to the British decimal penny as
Decimal decimal fractions were non-positional. However, counting rod fractions were positional. Qin Jiushao in his book Mathematical Treatise in Nine Sections (1247) denoted 0.96644 by J. Lennart Berggren notes that positional decimal fractions appear for the first time in a book by the Arab mathematician Abu'l-Hasan al-Uqlidisi written in the 10th century. The Jewish mathematician Immanuel Bonfils used decimal fractions around 1350, anticipating Simon Stevin, but did not develop any notation to represent them. The Persian mathematician Jamshīd al-Kāshī claimed to have discovered decimal fractions himself in the 15th century. Al Khwarizmi introduced fraction to Islamic countries in the early 9th