updated defn for 'stand off distance', made 'sD' use 'sd' definition to reduce duplication
updated defn for 'stand off distance', made 'sD' use 'sd' definition to reduce duplication

JacquesCarette/literate-scientific-software,JacquesCarette/literate-scientific-software,JacquesCarette/literate-scientific-software,JacquesCarette/literate-scientific-software,JacquesCarette/literate-scientific-software,JacquesCarette/literate-scientific-software,JacquesCarette/literate-scientific-software