Casella CEL CEL-278 - Manual (Page 13)

Figure 3 Control panel and display showing all indicators
(Normally, all indicators will not be displayed at the same time)
placed, or the external power supply must be checked or changed. Readings
taken while this indicator is showing should be discounted when absolute
accuracy is required.
3.3 Control Identities
The functions of the control switches and push buttons on the CEL-278 are
identified by the legends marked alongside them on the Instrument front
panel as follows, (see Figure 3).
RANGE: Off-Lo-Hi
This three position slide switch is the main on/off and range control for the
instrument.
No functions are performed in the "Off" position.
When this switch is moved from the "Off" position to apply power to the
instrument, a marker appears on the display adjacent to the AP (all pass)
legend.
CEL Instruments Ltd. CEL-278/2 Handbook Page 13