Toyota 2015 Prius Owner's Manual page 270

2-2. Instrument cluster
Switching the head-up display
Display items can be switched by pressing the "HUD" main switch.
Switching the turn-by-turn navigation display (if equipped)
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Speedometer
Displays the vehicle speed.
Speedometer and Hybrid Sys-
tem Indicator
Displays Hybrid System Indicator
under the speedometer.
( P. 227)
Off
When on, the indicator light on
the "HUD" main switch comes on.
On/off
When on, the indicator light on
the "NAVI" button comes on.