ESDU 77002 provides data for geometric gear design for gear ratios up to 10:1. Guidance on the choice between spur and helical gears is provided by considering the factors of noise@ end-thrust and cost. The choice of helix angle@ which is influenced by the type of machine used to cut the gears@ is discussed. Data are given that guide the user in the selection of the number of teeth in both pinion and wheel. The use of an addendum modification is explained and the effect of it on the tip diameter and pressure angle discussed. A design flowchart and accompanying calculation sheet in both British and SI units show how the equations and graphs are used in practical cases to select the dimensions of a gear pair. ESDU 68040 discusses the choice of appropriate materials (metallic or plastic).