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
Tenor guitar six string guitar. As string tension for any pitch increases with length, some have said these guitars cannot be tuned to the normal CGDA fifths tuning because the A string cannot be tuned to pitch without breaking. However, there are a variety of available methods for addressing this point and bringing the longer-scaled tenor guitar up to standard tuning and pitch: special string sets; strings extracted from a seven string guitar set; etc. Tenor guitars can also be tuned to a reentrant CGDA tuning where the A and sometimes the D are pitched an octave lower. The plectrum guitar is