Why are the values of my base report changing when I change the report from a text output to a spreadsheet output?

I am using report builder to display values generated from a query. The query output data is correct, and when my report is created as a text document, all values are correct. If I change nothing else but the report oputput format to a spreadsheet, the values of one column change.

Would you be a bit more specific? Are you talking about NUMERICAL (decimal) values? Maybe your SS column is set to a different default formatting than the one used by your query (and exported to text)?