CENTER Button (●)
Hold ~1 s to power on. Short press to select/confirm in menus. Hold ~3 s to power off. During startup countdown the CENTER button arms the zero sequence.
LEFT Button (◄ MODE)
Short press: cycle display modes Live → Peak → STEL → TWA → Alarm Limits. Hold ~2 s: enter main menu. In menu: LEFT navigates up through items.
RIGHT Button (► ACK)
Short press: acknowledge / silence alarm when gas has cleared. In menu: navigate down through items or go back / exit. Returns to Live mode from any display mode.