HP Deskjet 6127 Color Inkjet Printer - Manual (Page 45)

two-sided printing
Use one of the following methods to print two-sided documents:
●
automatic two-sided printing
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manual two-sided printing
automatic two-sided printing
To print two-sided documents automatically, the duplexer must be attached to the printer.
The duplexer only works with certain media types. For a list of supported media types, see two-
sided printing accessory specifications .
If you want to print a two-sided document on a media type not supported by the duplexer, see
manual two-sided printing .