For the following:
HP 504X CE250X Black Toner cartridge 10.5K page yield at 5% coverage
HP 504X CE251A Blue Toner cartridge 7K page yield at 5% coverage
HP 504X CE252A Yellow Toner cartridge 7K page yield at 5% coverage
HP 504X CE253A Red Toner cartridge 7K page yield at 5% coverage
HP CM3530 CM3530fs CP3520 CP3525 CP3525dn CP3525n CP3525x Laser Printer

Your Toner cartridge will shut down at every cycle of 10.5K printed pages, leaving you unable to print, even though there may be plenty of toner left in the cartridge.
Slash printing costs by simply replacing the chips which shut the cartridges down, to extend Toner cartridge life by up to 30-40%, or use the chip if you are refilling the cartridges, to get them working again.
Each chip lasts for one cycle of 10.5K printed pages, after which it must be replaced.