Those cheap black thermometer/hygrometers

How do you switch the temperature between C and F?

Some cant change and some you need to open up the back

Thanks Indo. I couldn't get the back off when I'd posted this. I'll have another try.

Found this review on Amazon, The review mentions C to F, but should work the way around .

(0°C × 9/5) + 32 = 32°F