I purchased this as a baby bottle warmer at the end of 2024 ❁ My baby refused to take a bottle, so I didn't end up making any formula. I boiled water twice, attempted to make formula, but gave up and stored it without use ❁ Power on confirmed ◎ 6-level temperature adjustment possible 45, 55, 65, 75, 85, and 100 degrees Celsius settings are available ◎ Purchased on Amazon ❁ ※It has been disinfected and cleaned, but water stains remain on the inside. Please check the photos. I haven't tried citric acid or baking soda, but you could try those. The surface of the stain is not rough.