[43.] Umbra Recta.
An-other maner of wyrking be umbra recta. Yif it so be that
thou mayst nat come to the baas of the tour, in this maner thou
schalt werke. Sette thy rewle upon 1 till thou see the altitude,
and sette at thy foot a prikke. Than sette thy rewle upon 2, and
5
beholde what is the differense be-tween 1 and 2, and thou shalt
finde that it is 1. Than mete the space be-tween two prikkes, and
that is the 12 partie of the altitude of the tour. And yif ther were
2, it were the 6 partye; and yif ther were 3, the 4 partye; et sic