Trèteaux Angles: P20a-DP
 P20a-DP = Adjacent Side (Head Cut) for Rotated Purlin Rafter Miter Angle on DP Side Of Hip Rafter on Face Perpendicular To Roof Surface, Lower Claw Angle
 Hip-Valley Roof Ratios Angle Formulas
- P20a-DP = arctan( sin (P19a ) ×  tan ( 90 - Valley Sleeper Saw Blade Bevel Angle )) 
- P20a-DP = arctan( sin (P19a ) ×  tan ( 90 - VSB ))  
 
 
 
 
The Trèteaux Angles Formulas for Hip Rafters Rotated into the Roof Surface Plane were developed by Sim Ayers and Joe Bartok.