Why do I need to use a temperature probe with my pH probe?

The chemical parameter of pH is a temperature dependent measurement. Only at 25 degrees Celsius / 77 degrees Fahrenheit is pH unaffected by temperature. So if your temperature is always 25 Celsius you would not need a temperature probe. In the same way pH 7.00 is also a stable point being unaffected by temperature changes.

So if your pH never varies from pH 7.00 even if temperature changes you would not need to do a temperature compensation calculation and would not need a temperature probe. In the real world however most likely the temperature and pH of your solution will vary. As a result the use of a temperature probe allows the pre-programmed microprocessor to do an Automatic Temperature Compensation, ATC, to give you a temperature adjusted pH that is always correct.