On the other hand, especially where a Roman numeral is considered a legally binding expression of a number, as in U.S. Even the post-renaissance restoration of a largely 'classical' notation has failed to produce total consistency: variant forms are even defended by some modern writers as offering improved 'flexibility'. Usage varied greatly in ancient Rome and became thoroughly chaotic in medieval times. This allows some flexibility in notation, and there has never been an official or universally accepted standard for Roman numerals. Roman numerals use different symbols for each power of ten and no zero symbol, in contrast with the place value notation of Arabic numerals (in which place-keeping zeros enable the same digit to represent different powers of ten). For the years of the current (21st) century, MM indicates 2000. MCM, signifying 'a thousand, and a hundred less than another thousand', means 1900, so 1912 is written MCMXII. Other common uses include year numbers on monuments and buildings and copyright dates on the title screens of movies and television programs. The notations IV and IX can be read as 'one less than five' (4) and 'one less than ten' (9), although there is a tradition favouring representation of '4' as ' IIII' on Roman numeral clocks. I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII
