Residual Pressure 4 : The pressure that exists in the distribution system, measured at the residual hydrant at the time the flow readings are taken at the flow hydrants
NFPA 291 Recommended Practice for Fire Flow Testing and Marking of Hydrants, 2002 ed. http://hep.ucsb.edu/people/hnn/wcp/NFPA291.pdf, (Recmm Prac: Fr Flow Tst and Marking of Hyd - Amer) {290 NFC}