If the volume of the container doesn't change, then the pressure of
the gas inside is proportional to its absolute temperature. That's
the temperature on the Kelvin scale.
0°C = 273.16 K
-1°C = 272.16 K .
So the gas pressure drops to
(272.16 / 273.16) = 99.63%
of what it was initially, a precipitous plunge of 0.366 percent.
