# Reliably Detectable Marks

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This section maps to Requirement 1.2-B
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Marks are determined valid and counted by the system if the amount of darker pixels in the bubble area exceeds a configurable threshold. This threshold can be adjusted to have a stricter or looser interpretation of what is considered a valid mark. The recommended and default threshold in the system is 7%, under which marks such as a light dot, a fold through a bubble, a stray mark outside of the bubble, or a small line just on the corner of a bubble will be considered invalid. Marks such as a completely filled bubble, half filled bubble, or an X in a bubble will be considered valid. Examples of invalid and valid marks along with the score for that mark (in green) are shown below. 

## Invalid Marks

<figure><img src="https://1186688720-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FqrzXyISkrU67zmViGRWG%2Fuploads%2FMeqInQWL5RUoJh98rdN7%2Finvalidmarks.png?alt=media&#x26;token=d940b4c3-c94d-4589-b96f-3fdb24ec2752" alt=""><figcaption></figcaption></figure>

## Valid Marks

<figure><img src="https://1186688720-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FqrzXyISkrU67zmViGRWG%2Fuploads%2F0ie695SA9CRAmeluys7Q%2Fvalidmarks%20(1).png?alt=media&#x26;token=86745a72-d25b-4d17-81c3-08869a5a6286" alt=""><figcaption></figcaption></figure>

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