Pascal (unit) dB SPL, or 20 µPa. The airtightness of buildings is measured at 50 Pa. The units of atmospheric pressure commonly used in meteorology were formerly the bar, which was close to the average air pressure on Earth, and the millibar. Since the introduction of SI units, meteorologists generally measure pressures in hectopascals (hPa) unit, equal to 100 pascals or 1 millibar. Exceptions include Canada, which use kilopascals (kPa). In many other fields of science, the SI is preferred, which means Pa with a prefix (in multiples of 1000) is preferred. Many countries also use the millibars. In practically all other
Sixteen-bar blues Sixteen-bar blues The sixteen-bar blues can be a variation on the standard twelve-bar blues or on the less common eight-bar blues. Sixteen-bar blues is also used commonly in ragtime music. Most sixteen bar blues are adapted from a standard twelve-bar progression. The standard twelve-bar blues progression is where each cell in the table represents one measure (or "bar"), "I" represents the tonic chord, "IV" the subdominant chord, and "V" the dominant chord. Twelve-bar progressions are formed by applying one of several formulae, including the following. One adaptation extends the first section of tonic chords (bars 1–4) by doubling or repeating