How do I enable High Altitude Brewing Mode on my Keurig K-Duo?
With the brewer plugged in and powered off, press and hold the BREW and OZ buttons together for 3 seconds. When enabled, 'ALT' will display on the screen and a mountain icon will appear. To disable it, repeat the same button combination. (Page 3)
From the official Keurig Descale Duo Coffee Maker manual, page 3
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