Columbia subject headings:
Abacus--History.
Astrolabes--History.
Astronomy, Medieval.
Harvard subject headings:
Abacus--History.
Astrolabes--History.
Astronomy, Medieval
Princeton subject headings:
Abacus.
Arithmetic--Early works to 1900.
Astrolabes.
Astronomy, Medieval.
Learning and scholarship--History--Medieval, 500-1500.