What are the digits on top of the housing for? Steve Giles November 10, 2020 16:54 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? Can I recycle the Flo Faucet filter cartridges? The Flo Faucet filter broke or is leaking after the installation. Is that normal? How much does it cost to have the filters in my Refill Station(s) replaced? How does the Flo Faucet calendar wheel work?