Which is the highest deduction for an error during gymnastics described in the tests?

The highest deduction for an error during gymnastics, as described in the tests, is indeed 0.5. This deduction typically applies to significant mistakes that substantially affect the performance, such as falling from the apparatus or exhibiting a severe lack of control. Such major errors can drastically impact the overall execution of a routine, and a 0.5 deduction reflects the seriousness of these mistakes in the context of judging.

In contrast, smaller deductions, such as 0.1, 0.2, and 0.3, are reserved for more minor errors that do not severely detract from the overall performance quality, such as slight form issues or minor balance checks. The scale of deductions is designed to clearly differentiate between minor and major errors, ensuring that gymnasts are appropriately penalized based on the impact of their performance issues.