Rafter, framing & T-bevel are useful types of this "geometric" tool
... Purlin Rafter Saw Blade 
Bevel Angles; Purlin Rafter Lip Cut Angles; Hip Rafter Roof Angles; Framing ... 
Types of Groin Vaults Supported; Semi-Circular Square Groin Vault; Semi-
Circular... [DOC] [TLE] Eyebrow Dormer Roof - Rafter Framing Calculator - SBE Builders [PAR] Online Tools ...