In the Roman numeral system, the basic "digits" are the letters I, V, X, L, C, D, and M which represent the same numbers regardless of their position. Symbols are placed in order of value, starting with the largest values. When the higher numeral is placed before a lower numeral, the values of each Roman numeral are added. When smaller values precede larger values, the smaller values are subtracted from the larger values, and the result is added to the total. Do not repeat I, X, and C more than three times in a row. (Number 4 on a Roman numeral clock is usually written as IIII. ) Symbols V, L, and D cannot appear more than once consecutively. Do not subtract a number from one that is more than 10 times greater: I may only precede V and X, X may only precede L and C, and C may only precede D and M.