Double whole note either of two ways: by a hollow oval note head, like a whole note, with one or two vertical lines on either side, as on the left of the image, or as the rectangular shape also found in older notation, shown in the middle of the image (; ). Because it lasts longer than a bar in most modern time signatures in common use, the breve is rarely encountered except in English music, where the half-note is often used as the beat unit . A related symbol is the double whole rest (double rest or breve rest), which usually denotes
Value of time can be examined. For example, if a traveler has a choice between a coach which takes six hours and costs £10, or a train which takes four hours and costs £30, we can deduce that if the traveler chooses the train, their value of time is £10 per hour or more (because they are willing to spend "at least" £20 to save two hours' travel time). The difficulty in narrowing down the "actual" value of time from a pair of choices means that hypothetical situations are generally used (the stated preference technique) to deduce values of time. The value of