A PC-4 Calculator (also known as the Pocket Computer) was utilized by Egon Spengler while he worked in the University's Paranormal Studies Laboratory.
After their encounter with the Library ghost at the New York City Public Library, the Ghostbusters returned to Columbia University. Egon used the PC-4 to make some calculations with data collected on the P.K.E. Meter. The computations confirmed that a ghost could be captured and held in storage indefinitely, assuming the ionization rate remained constant.