What are the digits on top of the housing for? They are a visual reminder (calendar wheel) to help you remember to change the cartridge every 3 months The numbers represent months and the dots represent weeks When you first install or change the cartridge, rotate the top to reflect 3 months from now This is when you should change the cartridge next Related articles Why does the water comes out as black at first? My Refill Station Isn't Working/Isn't Dispensing Water What contaminants does the FloWater Faucet Filter remove through its filtration process?