English Language (1828). In the United Kingdom, the influences of those who preferred the French spellings of certain words proved decisive. In many cases AmE spelling deviated from mainstream British spelling; on the other hand it has also often retained older forms. Many of the now characteristic AmE spellings were popularised, although often not created, by Noah Webster. Webster chose already-existing alternative spellings "on such grounds as simplicity, analogy or etymology". Webster did attempt to introduce some reformed spellings, as did the Simplified Spelling Board in the early 20th century, but most were not adopted. Later spelling changes in the UK had little effect on present-day US spelling, and vice versa. Punctuation Full stops and periods in abbreviations There have been some trends of transatlantic difference in use of periods in some abbreviations. These are discussed at Abbreviation § Periods (full stops) and spaces. Unit symbols such as kg and Hz are never punctuated. Parentheses/brackets In British English, "( )" marks are often referred to as brackets, whereas "[ ]" are called square brackets and "{ }" are called curly brackets. In formal British English and in American English "( )" marks are parentheses (singular: parenthesis), "[ ]" are called brackets or square brackets, and "{ }" can be called either curly brackets or braces. Despite the different names, these marks are used in the same way in both varieties. Quoting British and American English differ in the preferred quotation mark style, including the placement of commas and periods. In American English, " and ' are called quotation marks, whereas in British English, " and ' are referred to as either inverted commas or speech marks. Additionally, in American English direct speech typically uses the double quote mark ( " ), whereas in British English it is common to use the inverted comma ( ' ). Commas in headlines American newspapers commonly use a comma as a shorthand for "and" in headlines. For example, The Washington Post had the headline "A TRUE CONSERVATIVE: For McCain, Bush Has Both Praise, Advice." Numerical expressions There are many differences in the writing and speaking of English numerals, most of which are matters of style, with the notable exception of different definitions for billion. The two countries have different conventions for floor numbering. The UK uses a mixture of the metric system and Imperial units, where in the US, United States customary units are