The temperature -40 is the same in both scales. This gives an alternative conversion rule: to convert in ''either'' direction, first add 40; then multiply by 5/9 for °F->°C or 9/5 for °C->°F; then subtract 40. | The temperature -40 is the same in both scales. This gives an alternative conversion rule: to convert in ''either'' direction, first add 40; then multiply by 5/9 for °F->°C or 9/5 for °C->°F; then subtract 40. |