Calculations can be done in queries, they have built in functions like averaging, min, max etc as well as using VBA on a form.
The form values can also be used to filter the query results, for instance only values greater than the value on the form or between 2 dates.
So what data is going to be graphed, you say they can have 5 values but do not provide any examples.
So can you provide examples of any calculations that need to be carried out at examples of the data to be graphed?
Can you provide data or better still a dummy database with the data in the table(s)?
Once set up the graph will display whatever values are in the underlying query that provides the data.

Also which version of Access are you using?