Piper, Arthur (1944). "A graphic procedure in the geochemical interpretation of water-analyses". Transactions, American Geophysical Union. 25 (6): 914–928. Bibcode:1944TrAGU..25..914P. doi:10.1029/TR025i006p00914.
Rao, N. Srinivasa (December 1998). "MHPT.BAS: a computer program for modified Hill–Piper diagram for classification of ground water". Computers & Geosciences. 24 (10): 991–1008. Bibcode:1998CG.....24..991R. doi:10.1016/S0098-3004(98)00083-1.
Piper, Arthur (1944). "A graphic procedure in the geochemical interpretation of water-analyses". Transactions, American Geophysical Union. 25 (6): 914–928. Bibcode:1944TrAGU..25..914P. doi:10.1029/TR025i006p00914.
Rao, N. Srinivasa (December 1998). "MHPT.BAS: a computer program for modified Hill–Piper diagram for classification of ground water". Computers & Geosciences. 24 (10): 991–1008. Bibcode:1998CG.....24..991R. doi:10.1016/S0098-3004(98)00083-1.