Sharp UX-51 Operation Manual page 76

Memory
Substitute reception into memory
This is a back-up function which is automatically activated if your fax runs
out of paper or the paper jams.
When you have received a document in memory, FAX RX IN MEMORY
will appear in the display, alternating with OUT OF PAPER or PAPER
JAMMED. When you add paper or clear the paper jam, the stored documents
will automatically be printed out.
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