My Truncheon Meter gives varying readings! Why?

A. There are several explanations for this:

Please ensure the plastic shroud is fitted to the probe. Also make sure the nutrient solution is moving, you can use the Truncheon Meter to facilitate this.
Allow for temperature equalisation to take place. This can take up to 10 minutes especially if there is a major temperature difference between the Truncheon and the solution being measured.