Not to be confused with the PC-4 Calculator that is used by Egon in the scenes "Get Her!" and Terminated.
The Casio Micro-Mini Calculator was utilized by Egon Spengler while explaining what the third mortgage results would be. It was identified at GBFans by Alex Newborn. The calculator was not shown again in the film after the scene leaving the bank.
It is exactly noted as a Casio Micro-Mini M-810.