year 1976

The advanced calculator is a very interesting hybrid between the well known SR-51A and the later TI-55.To understand the position of the calculator you must remember that TI introduced the SR-40 with its one-chip design in 1976 but the advanced one-chip TI-55 later in 1977. The SR-51-II used the housing of them with the
very complex electronics of the earlier SR-51A. If you open the housing you’ll find a very interesting constructions with some stacked printed circuit boards (PCB) behind the LED display. To maximize density inside the calculator even the IC’s were soldered in small stacks.