"The spelling "expresso" is not used in the original Italian and is strictly incorrect, although it is common." The Oxford English Dictionary and Merriam-Webster call it a variant spelling. The Online Etymology Dictionary calls "expresso" a variant of "espresso". The Oxford Dictionary of American Usage and Style (2000) describes the spelling expresso as "wrong", and specifies espresso as the only correct form. The third edition of Fowler's Modern English Usage, published by the Oxford University Press in 1996, noted that the form espresso "has entirely driven out the variant expresso (which was presumably invented under the impression that it meant 'fast, express')". Shot variables The main variables in a shot of espresso are the "size" and "length". This terminology is standardized, but the precise sizes and proportions vary substantially. Cafés may have a standardized shot (size and length), such as "triple ristretto", only varying the number of shots in espresso-based drinks such as lattes, but not changing the extraction – changing between a double and a triple requires changing the filter basket size, while changing between ristretto, normale, and lungo may require changing the grind, which is less easily accommodated in a busy café. Size The size can be a single, double, or triple, using a proportional amount of ground coffee, roughly 7, 14, and 21 grams; correspondingly sized filter baskets are used. The Italian multiplier term doppio is often used for a double, with solo and triplo being more rarely used for singles and triples. The single shot is the traditional shot size, being the maximum that could easily be pulled on a lever machine. Single baskets are sharply tapered or stepped down in diameter to provide comparable depth to the double baskets and, therefore, comparable resistance to water pressure. Most double baskets are gently tapered (the "Faema model"), while others, such as the La Marzocco, have straight sides. Triple baskets are normally straight-sided. Portafilters will often come with two spouts, usually closely spaced, and a double-size basket – each spout can optionally dispense into a separate cup, yielding two solo-size (but doppio-brewed) shots, or into a single cup (hence the close spacing). True solo shots are rare, with a single shot in a café generally being half of a doppio shot. In espresso-based drinks in America, particularly larger milk-based drinks, a drink with three or four shots of espresso will be called a "triple" or "quad", respectively. Length