To ensure the long-term accuracy of your Bluelab EC meters, we recommend cleaning and testing them regularly. All Bluelab EC pens and meters are factory calibrated, so recalibration is not necessary. Instead, clean the Bluelab EC probe and verify successful cleaning using the Bluelab 2.77 EC Standard Solution - 250ml. It is recommended that you clean and test the EC meter every 30 days. All Bluelab products come with detailed cleaning and care instructions. The Bluelab 2.77 EC Standard Solution - 500ml is essential for use with all Bluelab EC products.