HP HP-20S - Environmental Limits; Determining Calculator Service Needs

Erasing Continuous Memory
If the calculator fails to respond to keystrokes and you are unable to
restore operation by following the reset instructions, clearing memory
may restore calculator operation. Press and hold down [C], then press
and hold down both and [Z+]. When you release them, all mem-
ory is cleared. The ALL CLr message is displayed.
Memory can inadvertently be cleared if the calculator is dropped or if
power is otherwise interrupted.
Environmental Limits
To maintain product reliability, you should avoid getting the calcu-
lator wet and observe the following temperature and humidity limits:
B Operating temperature: 0° to 45°C (32° to 113°F).
B Storage temperature: —20° to 65°C (—4° to 149°F).
B Operating and storage humidity: 90% relative humidity at 40°C
(104°F) maximum.
Determining if the Calculator Requires
Service
Use these guidelines to determine if the calculator requires service. If
these procedures confirm that the calculator is not functioning prop-
erly, read the section “If the Calculator Requires Service” on page 118.
114 Assistance, Batteries, Memory, and Service