The accuracy of a Brix refractometer in determining fruit ripeness depends on the type of fruit being tested. Generally, Brix refractometers are most accurate for fruits with a high sugar content, such as grapes, apples, and oranges. For fruits with a lower sugar content, such as strawberries and blueberries, the accuracy of the Brix refractometer may be lower. Additionally, the accuracy of the Brix refractometer can be affected by the age of the fruit, the variety of the fruit, and the environmental conditions in which the fruit was grown.