The conversion

1°F = −17.22°C

°C = (°F − 32) × 5/9, so (1 − 32) × 5/9 = −17.22.

As an outdoor air temperature, 1 °F sits in the bitter band. The other scale is on the dial beside it in the app, so a reading like this needs no conversion at all.

Convert something else

68°F

The range either side

Neighbouring values, for when the number you actually wanted was a degree or two away.

Fahrenheit to Celsius either side of 1 °F.
FahrenheitCelsius
−4 °F−20 °C
−3 °F−19.44 °C
−2 °F−18.89 °C
−1 °F−18.33 °C
0 °F−17.78 °C
1 °F−17.22 °C
2 °F−16.67 °C
3 °F−16.11 °C
4 °F−15.56 °C
5 °F−15 °C
6 °F−14.44 °C

The other direction

−17.22 °C converts back to 1 °F, which is the same relationship read the other way. Going from Celsius to Fahrenheit, multiply by 9/5 first and then add 32. Adding first is the usual mistake.

The full converter handles any value, in either direction, including kelvin, and shows the formula as it works.