Terminated: unknown
Firstly you can play music (top-left slider in the middle position), either your own creations using the numeric keypad, or the pre-programmed song "When the Saints Go Marching In" my pressing the blue key. In this mode the calculator also be used as a calculator.
Secondly, when the top-left slider is all the way to the right you can perform calculations and play the "Space-Invaders" game as well. Press the blue key to start the game. A string of numbers will appear from the right. Use the "AIM"-key to match the leftmost number and the "FIRE"-key to eliminate the number from the string of numbers. Quite difficult actually, one needs to be quite speedy.
This page on liquidcrystal.co.nz (link valid 2024-01-13) has some details, as well as links to similar calculators.
The plastic of this calculator has turned quite yellow. It originally was almost grey.