To express 25.00°C as a temperature in kelvins, we use eqn 1.4 to write
T/K = (25.00°C)/°C + 273.15 = 25.00 + 273.15 = 298.15
Note how the units (in this case, °C) are cancelled like numbers. This is the procedure
called ‘quantity calculus’ in which a physical quantity (such as the temperature) is the
product of a numerical value (25.00) and a unit (1°C); see Section F.7. Multiplication of
both sides by the unit K then gives T = 298.15 K.