A "rāga" has a given set of notes, on a scale, ordered in melodies with musical motifs. A musician playing a "rāga", states Bruno Nettl, may traditionally use just these notes, but is free to emphasize or improvise certain degrees of the scale. The Indian tradition suggests a certain sequencing of how the musician moves from note to note for each "rāga", in order for the performance to create a "rasa" (mood, atmosphere, essence, inner feeling) that is unique to each "rāga". A "rāga" can be written on a scale. Theoretically, thousands of "rāga" are possible given 5 or more notes, but in practical use, the classical tradition has refined and typically relies on several hundred. For most artists, their basic perfected repertoire has some forty to fifty "rāgas". "Rāga" in Indian classic music is intimately related to "tala" or guidance about "division of time", with each unit called a "matra" (beat, and duration between beats).