Here Begins the Fourth Chapter on the Subtraction of Lesser Numbers from Greater Numbers

Abstract

However when one will wish to subtract one number from another, then he writes the lesser number beneath the greater, locating similar places below similar, and he begins to subtract the first figure in the lesser number from the first in the greater; and he puts the excess of the number over the first figures. And next he subtracts from the second, and he puts the difference above the second, and the third above the third. And the differences of the others in order, always putting the differences. And when the subtraction is not valid for the figure of the lesser number from the figure of the same place of the greater number for the reason that the figure in the lesser number will be larger than the figure in the same place in the greater number, then the figure of the greater number is added with the tens, and from the sum of the numbers, the figure of the lesser number will be subtracted. And for the sum with the said tens the units will be kept in hand. And for the following figure of the lesser number above added and built quantities of the upper figure of the same place, if it is made possible, will be subtracted, but however from the added tens, as we said above, it is subtracted; and thus up to the last figure of the lesser number operating by steps; and if the greater number is less in the place above the figure showing in the same place, it will be put in the end. And thus will be had the difference of any subtracted numbers.