Sthayi
The register or octave in which a svara sounds.
The three commonly discussed registers are mandra (lower), madhya (middle) and tara (upper).
Reading octave marks
Sa in different octaves shares a name but has a different pitch height. S marks middle Sa and Ṡ marks upper Sa. A dot below a letter marks the lower register.
Follow the notation key for the music you are reading. Related: Svara · Arohana