Endnote 21
Part I, §18, l. 8.  compowned by 2 & 2.  This means that in the best astrolabes, every almicantarath for every degree of latitude was marked; as may be seen in Metius.  In others, including the one given by Chaucer to his son, they were marked only for every other degree.  See Part II. sect. 5, l. 2.