Although notes are an important part of rāga practice, they alone do not make the rāga. A rāga is more than a scale, and many rāgas share the same scale. The underlying scale may have four, five, six or seven tones, called "swaras" (sometimes spelled as "svara"). The "svara" concept is found in the ancient "Natya Shastra" in Chapter 28. It calls the unit of tonal measurement or audible unit as "Śruti", with verse 28.21 introducing the musical scale as follows,