An unusual item, this module selector allows four solid state modules to be connected simultaneously to the TI-59. Only one of the modules can be active at any given time and the selection is made through a rotary switch.
The device works with the TI-58 and 58C also. The module selector is designed to be placed in the battery charging compartment of a PC-100 (A or C) printer and is connected to the calculator through a flat cable as can be seen in the images.
Very rare device!