Fujitsu FP-510II User Manual page 22

Caution: Red or blue printing on two-color thermal paper has an inferior
preservation characteristic that is equivalent to that of normal
thermal paper.
Caution: Printouts on label paper or thick paper may contain blurs or voids,
depending on the humidity and other environmental conditions.
Adjust the print speed and print density as appropriate for the type
of paper used. (See "C-3 Setting Up the Printer" in Appendix C,
"Special Modes.")
In particular, note that the paper transport accuracy may be
negatively affected by printing a barcode in the top margin at the
beginning of paper transport or in the Lower margin at the end of
paper transport.
Caution: Gray scale printing cannot be printed clearly with the paper more
than 85um thickness and label paper.
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