There are several books explaining the notation symbols for harp.The largest so far, just under 140 pages written in 1985 and perhaps updated since then, is “Writing for the Pedal Harp” by Inglefield and Neill, and includes a recording where a harpist demonstrates the many symbols in the book. Not only symbols commonly used, but variants are also included, as well as information on amplification and other harp issues.An extensive bibliography, and index