The display will show a three digit random number. You can, but don't have to, try to form a winning number by holding one, two or three digits and pulling the handle again. Once you've kept the ones you want to or if you want to throw all of them away, press E to pull the arm of the bandit again.
Display shows the newly formed number.
Repeat steps 4-6 until your money runs out. You will be shown a display of all zeros when that happens. Go back to step 3 at that point. You may then hold new ones in step 5. Keycodes are for the HP-67.