There is a calculator that will layout any T branch at any angle and also layout the hole and find the exact angle!  This is a TRUE Hand Held LAYOUT CALCULATOR.
I consider this unit a tool rather than a computer because you always have it nearby and it is an excellent Companion for the Bench, Shop, Field and Office.
It will layout Intersecting TEE's including the HOLE layout,  Cone's, Square to Rounds, Round Elbows, Pipe, Tube & Sheet Metal Round Offsets, Custom Kitchen
& Fireplace Hoods, Handrails, Crickets & Saddles and much more. Its very user friendly. It always reads dimensions in DECIMAL form 1st,  then in FRACTIONAL
Form 2nd,  to the closest 1/32",+/- 1/64".  This is for the person that doesn't know his/her Decimal readouts. It also has Utility programs for Drill & Tap sizes,
Metric Conversion, Arc's & Radius's, Solves Oblique & 90 deg. Triangles, Pulley sizes including RPM and Belt lengths and more. A good tool for company shop
employee's to have.  This TOOL will easily save time on Bench & Field Layout. Click on the WebSite below to see more about this tool, you can view all the
pages from the manual which is used like a computer Monitor if needed for Visual Instruction, direction and hole Layouts.  Be sure to read the "NOTES" in
the Layout Manual Page section, they help things make sense. These programs were actually used to layout these fittings & handrail below.
The Square to Round program was used on the 1st item.  The Radius Stretch, Round Elbow & the Square to Round programs were used on the Jet Engine Test
Cell Exaust, (ready to be insulated).  The Modual2 & the 90 deg. Triangle programs were used on the handrails fabricated by a local Custom Sheet Metal Shop
in San Diego, CA. (Excellent crafstmanship).  It's NOT a toy!!

http://www.sheetmetallayoutcalculator.com