I think your description is missing something. Why does pulling up a found set of 31 records require a summary of a summary instead of just summarizing the original Used Time field across a found set of 31 records? Is this, perhaps, data from a table that is related to the table where you have just found 31 records? If so, you can define a calculation field that refers to the value of this original summary field and then you can summarize the calculation field.
I have the table "Virksomhed" in which all of our customer records are stored.
I do a manuel search on "Customer User" and "Customer Type", doing a find.
I have created a separate table called "Log" ( Virksomhed-------<Log ), which creates a record with relationship to the given company, to date and log the work we've done on every customer through out the year timewise.
Example, I've made 3 records in "Log" and input the time i've spend on the work, creating the 3 records, let's say 3 hours of work on each record.
Now, I've already made a summery field called "Total Time" which summarizes the total time spent on each company.
Now for the question, how do I make a total of time spent based on my found set, the 31 records, since I can't make a summery field out of another summery field?
I did mention using a calculation field to copy the summary field value so that your second summary field can summarize the calculation field. But let's back up a second first:
You perform a find on Virksomhed and need a total from all related records in Log, correct? A calculation field in Virksomhed can also use Sum to compute the total related records in Log and then a summary field can compute the total.
Or you can perform this find on the Log layout rather than the Virksomhed layout, sort your records and your exisitng summary field now can show a total for each related record in Virksomhed by putting fields from that parent table and the summary field into a sub summary layout part. If you don't want to list the individual log entries--preferring a single row of data with a sub total for each related record in Virksomhed, use a layout where the body layout part has been removed so that you just have sub summary layout parts.
Here's a tutorial on summary reports: Creating Filemaker Pro summary reports--Tutorial