Hip or Valley, “Jack Rafters”
— with other than 16” on-center
You’re again working with a 7-in-12 Pitch and
the Run of the common rafter is 30 feet 9 inches.
You want to calculate the length of your jack
rafters at 18 inches o.c. You’ll need to enter 18
inches o.c. into the [Jack] key before you find the
lengths of the jacks:
COMMENTS KEYSTROKES
Clear calculator [On/C] [On/C]
Enter Pitch 7 [Inch] [Pitch]
Enter Run of common 30 [Feet] 9 [Inch] [Run]
Enter 18” o.c. * 18 [Jack]
Recall to verify 18” o.c. [Rcl] [Jack]
Answer: 18 IN JK
Find 1st Jack [Jack]
Answer: 33 FT 10-23/64 IN
Find 2nd Jack [Jack]
Answer: 32 FT 1-33/64 IN
Find 3rd Jack [Jack]
Answer: 30 FT 4-43/64 IN
Find 4th Jack [Jack]
Answer: 28 FT 7-27/32 IN
Etc., Etc.
Repeat, until all jacks are found, or when
calculator displays “0 FT 0 IN.”
* You do not need to label the 18 as “inches” — the
calculator will automatically assume an inch format.
User’s Guide — 45
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