How do I know when an ink cartridge needs to be replaced?

• When the printer's red Error light flashes, an ink cartridge is low on ink. This is a good time to make sure you have a new cartridge handy. When the Error light stays on, the cartridge is empty and will need to be replaced. The Error light also flashes when there is a paper jam so make sure to check your paper before changing the ink cartridge.
  
  You can click on the EPSON Status Monitor to check which cartridge is low or empty. To check your ink supply, do one of the following:
  
  Windows:
  Double-click the printer icon on your taskbar (in the lower right corner of your screen). You see a window showing ink levels. You can also double-click the Ink Monitor icon on the taskbar. The window that appears lets you check ink levels and also order cartridges online. Just click the Buy Now button to launch your web browser.
  
  Macintosh:
  OS 8.6 to 9.x:
  Choose File > Print. Click the ink icon.
  
  OS X:
  Choose Applications>EPSON Printer Utility>C62 Series>EPSON Status Monitor.