Mandolin are used. Usually, courses of 2 adjacent strings are tuned in unison. By far the most common tuning is the same as violin tuning, in scientific pitch notation G–D–A–E, or in Helmholtz pitch notation: g–d′–a′–e″. Note that the numbers of Hz shown above assume a 440 Hz A, standard in most parts of the western world. Some players use an A up to 10 Hz above or below a 440, mainly outside the United States. Other tunings exist, including "cross-tunings", in which the usually doubled string runs are tuned to different pitches. Additionally, guitarists may sometimes tune a mandolin to
Viol for the lowest-pitched bass strings on viols, and on many other string instruments as well. Viols are fretted in a manner similar to early guitars or lutes, by means of movable wrapped-around and tied-on gut frets. A low seventh string was supposedly added in France to the bass viol by Monsieur de Sainte-Colombe (c. 1640–1690), whose students included the French gamba virtuoso and composer Marin Marais. Also, the painting (1618) by Domenichino (1581–1641) shows what may be a seven-string viol. Unlike members of the violin family, which are tuned in fifths, viols are usually tuned in fourths with a major