Arbor doesn't allow you to input negative or minus values into Assessment Marksheets, or to import them via spreadsheet. This applies to all assessment types - Summative, Ad Hoc and Formative.
Once you refresh or return to the marksheet page, any negative values you input are wiped.
If you want to show the difference between two columns on the marksheet to show a student is behind (such as the difference between reading age and predicted reading age), you can:
- add a custom field using custom marksheets
- use the Summative Assessments > Analysis > Statistics page to calculate the progress gap