Yes, all Calculator modules are physically interchangeable. You just have to be careful about re-arranging the keyboard keys to match the version you are installing (reversing the positions of the "C" and "=" keys, and the positions of the "R" and "S" keys, depending on whether a 901 or 902/3 module is going in). DON"T open a Calculator (or any other Pulsar, for that matter) unless you are electrically grounded (or it's a rainy, high-humidity day, to eliminate any possibility of introducing a static charge into the electronics...something that may have killed as many modules as leaking batteries), and NEVER set an uncased Calculator module face-down on any surface, or you can kiss most of the display wire-bonds good-bye.