The name was later changed to PS - Plot , and changed again to the current PSI - Plot .
PSI - Plot was developed by Poly Software International , Inc. in September 1992 , under the name TechPlot for MS - DOS .
The TechPlot was later changed to PS - Plot , and changed again to the current PSI - Plot .
PSI - Plot was developed by Poly Software International , Inc. in September 1992 , under the name TechPlot for MS - DOS .