Fernando Sor Studies from opp. Sor's music education as a youngster was pretty conservative and quite thorough. This accounts for his pristine compositional style. In a long and varied career, Sor was always true to his core conviction that the guitar needed a professional-level repertoire.
Instrumental studies are particularly nasty as composition.
Throughout all of music history, most composers don't really try to compose instrumental studies. They're tricky stuff to get right. Well, Sor did it perhaps better than anyone. The liner notes contain interesting information on the different periods of Sor's life from which sprang these different Opus numbers. The earliest is Op. 6, from which we hear eight studies.