citation 66 4987 5Model: Citation (66-4987-5)
Battery: 9 volt
Adapter: AC9180
Year: 1977
Chip:  TMS0972        
The TMS0952 introduced with the original design of the M4986 was soon replaced with the TMS0972, a pin-compatible design dropping the additional resistors and capacitor and further reducing the manufacturing costs of the M4986 series. This contribution of cost cutting had a side effect for the customer, Texas Instruments decided to use with the TMS0972 an 8-digit LED display instead of the previous 9-digit display. While the 9th (leftmost) digit was originally used only for the negative sign and didn't impact most calculations, should you try this example: 

• 11111111 [-] 23456789 [=] - TMS0952: -12345678
• 11111111 [-] 23456789 [=] - TMS0972: -.1234567 (flashing)