HP HP-67

50 Display Control
Calculator Overflow
When the number in the display would be greater than 9.999999999
X 10%, the HP-67 displays all 9’s to indicate that the problem has
exceeded the calculator’s range. For example, if you solve (1 X 10%)
X (1 X 10%), the HP-67 will display the answer:
Press Display
CLX
=33 49 1.000000000 49
D 508 1.000000000 99
But if you attempt to multiply the above result by 100, the HP-67
display indicates overflow by showing you all 9’s:
Press Display
100 9.999999999 99 | Overflow indication.
Error Display
If you happen to key in an improper operation (or if a magnetic card
fails to read properly) the word will appear in the
display.
For example, if you attempt to calculate the square root of -4, the
HP-67 will recognize it as an improper operation:
Press Display
+@D
0=
Pressing any key clears the error and is not executed. The number
that was in the display before the error-causing function is returned to
the display so that you can see it.