Columbia subject headings:
Astrolabes--History.
Astronomy, Medieval--Instruments.
Ciphers--History.
Manuscripts, Medieval.
Numerals, Writing of--History.
Numeration--History.
Harvard subject headings:
Astrolabes--History.
Astronomy, Medieval--Instruments.
Manuscripts, Medieval.
Numerals, Writing of--History.
Numeration--History
Princeton subject headings:
Astrolabes--History.
Astronomy, Medieval--Instruments.
Ciphers--History.
Manuscripts, Medieval.
Numerals, Writing of--History.
Numeration--History.