Both of these features are electronic filter replacement indicators that remind you when to replace your cartridge. The BRITA® MEMO keeps track of the time since you last changed your filter element. Just press the button to start the countdown. It automatically reminds you when it's time to change the filter element. BRITA® METER uses three factors to determine the optimal time to replace your cartridge: amount of water that has been filtered, water hardness, and time since the cartridge was last replaced.