# Reliably Detectable Marks

Marks are determined valid and counted by the system if the amount of darker pixels in the bubble area exceeds a configurable "definite" mark threshold set in the [election-package](https://docs.voting.works/vxsuite-tdp-v4/system-overview/election-package "mention") system settings file. This mark threshold can be adjusted to have a stricter or looser interpretation of what is considered a valid mark. On both VxScan and VxCentralScan, the voting system does not process any marks as ambiguous. All marks are either valid or invalid.

The recommended and default threshold is 7%. With this threshold setting, hand marked paper ballot interpretation detects a valid mark per the mark conditions described by VVSG 1.1.6-H.

At this default threshold, 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. 

The mark threshold set on a scanner can be checked by an election official at any point by viewing the readiness report for that device as described in [diagnostics](https://docs.voting.works/vxsuite-tdp-v4/system-overview/diagnostics "mention") (see also [VxScan Diagnostics](https://app.gitbook.com/s/JtZutzGTdCzsGITrdiph/vxscan/vxscan-diagnostics "mention") & [VxCentralScan Diagnostics](https://app.gitbook.com/s/JtZutzGTdCzsGITrdiph/vxcentralscan/vxcentralscan-diagnostics "mention") in the user manual).

### Invalid Marks

<figure><img src="https://629495352-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZ4bC0rbmogHEUUuMLAUa%2Fuploads%2Fckb629mpVBJExF8sEtbg%2Fimage.png?alt=media&#x26;token=2419236d-769e-4c94-92dc-90f4f7c4f31a" alt=""><figcaption></figcaption></figure>

### Valid Marks

<figure><img src="https://629495352-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZ4bC0rbmogHEUUuMLAUa%2Fuploads%2Fju8Po2B8PdSy9U6QQJkK%2Fimage.png?alt=media&#x26;token=83e6708c-7c33-43b4-9a6a-1f335f34c017" alt=""><figcaption></figcaption></figure>

### Marginal Marks

The system also supports setting a marginal mark threshold for flagging ambiguous marks close to but not quite over the definite mark threshold. If a marginal mark threshold is set and marginal mark adjudication is enabled, the definite mark threshold can be increased without having to worry about completely missing marks.