It is a pure coincidence. Nothing special.
The point at which the Celsius and Fahrenheit scales meet is -40 degrees. -40 degrees Celsius is equal to -40 x 9 = -360 / 5 = -72 + 32 = -40 degrees Fahrenheit.
The scales of degrees Celsius and Fahrenheit are equivalent at -40 degrees.
-40 degrees is the temperature at which the Fahrenheit and Celsius scales coincide.
Was that on purpose? Because it just so happens that -40 is where the two meet! -40 degrees Celsius = -40 degrees Fahrenheit. Was that on purpose? Because it just so happens that -40 is where the two meet! -40 degrees Celsius = -40 degrees Fahrenheit.
The temperature when both the Celsius and Fahrenheit scales are the same is - 40 degrees.
The scales of temperature cannot all meet, as the Kelvin and Celsius scales have the same size degrees but different zero points. Absolute Zero is 0° Kelvin, and equal to -273.15 °C or -459.67 °F. Because the Celsius and Fahrenheit scales are offset by 32° at their starting points (freezing point of water), the two scales do have a common numerical point at -40° (minus 40 degrees). (see related question)
-40 degrees is the same in Fahrenheit and Celsius.
The temperature where Celsius and Fahrenheit are the same is -40 degrees.
The temperature at which Celsius and Fahrenheit scales are equivalent is -40 degrees.
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The temperature reading that is the same on both Celsius and Fahrenheit scales is -40 degrees.
At -40 degrees on both scales.