I think it is an estimate only, but to be sure you should speak with 2nd Level: 1-800-821-2797
Looking at Reports>Device>Device Statistics in the B230 web interface shows Supply Information as follows:
Are "Days Remaining" an estimate of how long the cartridge will last based on actual printer usage? Or does it indicate an absolute timeframe within which the cartridge must be replaced?
Is there a way to reset the days remaining counter given that pages remaining are 700? Will the printer simply stop working when the days remaining counter reaches zero?