Product Code:SAE ARP427 Title:Pressure Ratio Instruments Issuing Committee:A-4 Aircraft Instruments Committee Scope:This Aeronautical Recommended Practice covers two types of two unit Pressure Ratio Instruments each of which consist of of a Transducer and an Indicator. The Transducer computes the ratio of two pressures and converts this ratio to a synchro electrical signal which is transmitted to the Indicator.Type I - All material in this document applies to this classification only.Type II - Additional material for this classification will be added to superseding issues as the state of the art permits.