I want to sum values of each 7 records only and not to sum all records of a database.

How could I do that?

Thank you

 

Is there a value that distinguishes those records? If not, you might build a workflow that allows the user to select records to be summed. 

1 hour ago, Eduardo Homem said:

sum values of each 7 records only

That can be read in many ways. Why don't you add more details and an example. And also explain why you need this.

In general, records can be grouped by some common value (for example, by the result of integer-dividing their serial number by 7), and then you can use a summary field to produce the total of each group.

 

Ah, you're a much more careful reader than I am, @comment. Didn't catch the possible need for a sub-summary.