HP HP-21 - Overextended Calculation

24 Controlling The Display
Overextended Calculation
When the display would be greater than 9.9999999 x 10%, the
HP-21 displays all 9’s to indicate that the problem has ex-
ceeded the calculator’s abilities for display. For example, if
you solve (1 x 10%*) x (1 x 10%°), the HP-21 will display the
answer.
Press Display
49 1.0000000 49
50 [x] 1.0000000 99
But if you attempt to multiply the above result by 100, the
HP-21 display indicates that it has overextended by showing
you all 9’s.
Press Display
100 [x] 9.9999999 99