 Nonetheless, it was not inaccessible.As Andrea Bianco urged, navigators should "know how to multiply well and divide well" ("saver ben moltiplichar e ben partir") It is here where we see the important interface of commerce and navigation.The mathematics of commerce – Arabic numerals, multiplication, division, fractions, the tools needed to calculate purchases and sales of goods and other commercial transactions – was essentially the same as the mathematics of navigation.