Palestine Standards Institution 
pounds per square inch 
Program Specific Information 
Plasma Source Instrument 
Performance Systems International 
Proliferation Security Initiative 
Personnel Security Investigation 
Personnel Security Investigations 
Population Services International 
Product Support Integrator 
Protocol Specific Indication 
Packet Switch Interface 
Packet Switching Interface 
Packetnet System Interface 
Per Square Inch 
Planning Systems Incorporated 
Plan-Speed Indicator 
Power Static Inverter 
Preprogrammed Self-Instruction 
Packet Switched Interface 
Packetnet Systems Interface 
Paid Service Indication 
Paul Scherrer Institute 
Pavement Serviceability Index 
Personalized System Of Instruction 
Pharmaceutical Society of Ireland 
Phase Shift Interferometer 
PI Scientific Instrument 
Planetary Science Institute 
Pneumonia Severity Index