(2) End cut use same numbers as for plumb cut of hip or valley but invert square.
f. Reduction for ridge. Measure straight back from plumb cut ½ diagonal thickness of ridge.
g. Backing of hip. (Cf. column 21) Take 12" (rise of common rafter) on the tongue and 20-13/16" on the blade scribe along the tongue for angle of backing.
h. Drop of hip when no backing is given. (Cf. column 23) Reduce at seat cut 9/16", measured at right angles to seat cut.
5. To Lay Out Jacks.—
a. Plumb cut. Same as that for the common rafter!
b. Side cut. (Cf. column 14) Take 12" on the tongue and 16.97" or 17" on blade (.97" = 1", columns 3 and 4), scribe on the blade.
Scribing along the tongue will give the face cut of roof boards, also of plancher.
c. Length. Jacks set 24" centers, beginning with shortest jack =2' 10" (column 19). Second shortest jack = length of shortest increased 2' 10", etc.
Beginning with longest jack = length of common rafter diminished by 2' 10", etc.