This is a weak point of the system. When the parsing fails the system informs the user that it failed then attempts to show the best parsing of the formula. However, there is no help offered to suggest what the problem could be, though to automatically determine what is wrong with a user's formula could be impossible. The best that could be done would be to determine common errors, such as mismatched brackets, and provide suggestions in these cases.
Errors in recognition and stroke grouping are provided through the use of annotated bounding boxes. These worked well, though occasionally participants in the user testing did not notice that characters were incorrectly recognised.
Simple recovery from recognition and stroke grouping errors is available through the modify stroke groups and modify character modes. Recovery from parsing errors is possible through the select and move mode that allows users to rearrange their formulae, though guidance as to what needed to be done to recover from parsing errors does not exist.