Well, changing the temperature scale from Celcius to Fahrenheit (or vice versa) varies from model to model. The instructions for Braun Thermoscan 3,5, and 7 are as follows. Braun Thermoscan 3 IRT3030 When the thermometer is off, simply press and hold the start button. This will help the thermometer to come on. After about 3 seconds, you will be able to see an F or a C appear on the screen. If you continue holding on the Start button, it will toggle between the two options. When the temperature scale/unit of measurement that you desire displays on the screen, release the button. Braun Thermoscan 5 IRT6020 Simply press and hold the start button. When you do this, the thermometer will come on and display the start screen. And then you'll get to view all of the symbols on the display. Just continue holding the button down. It will display C or F for one second and then change to SET for one second. This pattern will continue displaying as you continue to hold down the start button. F -> SET -> C -> SET. When the setting that you need appears on the screen, select the option you want and then release the start button. Braun Thermoscan 7 IRT6520 The thermometer should be off. Then press and hold the power button to turn it on. After 3 seconds, the screen will display and switch between C / SET / F / SET. Once the temperature scale that you desire is displayed, release the power button. It will beep to select the temperature scale and then turn off.