The fact that you did not use a value list may create issues with your data if you have accidentally introduced some data entry errors into this field.
Some types of aggregate calculations, Sum, Total, average, Standard deviation, Minimum, Max... can be applied to a group of such records by defining a summary field and setting up a summary report where you sort records on this field to group all the records by this value and use a sub summary layout part to show the sub total, average, etc for that group of records. Depending on your layout design, you can list the individual records that make up that value or just have one row of data for each possible value in this field with a sub total for each.
Here's a tutorial: Creating Filemaker Pro summary reports--Tutorial
Another approach is to use a relationship that matches to all records with a specific value in this field. That relationship can be a self join that matches the current record to all other records with the same value in this field. Or you can set up a separate field where you select a value and then the relationship matches to all records of the specified value. Either approach enables you to set up calculations (in fields, conditional formats, hide object when, script steps...) that reference data in the related group of records.
A third approach is essentially the same as the second, but you manage the relationships via SQL in an ExecuteSQL() function call.