Epson EPI-4000 User Manual page 37

Assembling the Printer
4. Close the ink compartment cover.
Note: Each ink cartridge contains enough ink to print up to 1000
average letter size pages. Pages with graphics or dense text use
more ink. The first ink cartridge you install may print fewer
pages because some of the ink is used to fill the ink feeding
system.
When to replace a cartridge
The indicator lever at the end of each cartridge shows you when it's
time to replace the cartridge. The lever moves from F (full) to E
(empty) as the ink is used. See Chapter 5 for more information on
replacing an ink cartridge.
1-20 Setting Up the Printer