The temperature scale you refer to is the Celsius scale, which uses degrees Celsius (°C) as its unit. The difference in temperature between 3°C and 6°C is 3 degrees, which is half the difference between 0°C and 6°C (6 degrees). Doubling the temperature in Celsius degrees means adding 100 degrees to the temperature value. For instance, doubling the temperature from 0°C would result in 100°C.

In contrast, the scientific temperature scale, known as the Kelvin scale (K), uses the absolute zero (-273.15°C) as its reference point. Doubling the temperature on the Kelvin scale means multiplying the temperature value by 2. Therefore, doubling the temperature from 3°C (276.15 K) would result in 6°C (279.15 K), which is twice the original temperature on the Kelvin scale.