Do you want to add a sequential number to the form - or just to the replies in the Response Table?
I would like both. The response table already has a time stamp to the seconds. If I could figure out how to get that to show on the form I could just use that as the PO. But any way to get a unique PO would be fine for our purposes.
I am not aware of any way to display a sequential number on the form created in FormsCentral (ie each opening increments by 'x'). I am willing to be corrected, but I think it unlikely.
Not approved by Adobe - but two methods that have worked for me and I have suggested previously in this Forum which have worked for other authors.
a) Export the response table to Excel, highlight the Time Date stamp column and format that column as number. (it'll convert the date time field to a number, which'll be unique unless you get a huge volume of concurrent responses. or;
b) Open the View Responses tab ~ move mouse over the letter in the left most column header (i.e.A) - you will see a dropdown arrow appear ~ click on the arrow and choose Insert Column (either before or after - your choice) - now think of the response table as an excel spreadsheet ~ in the first cell (e.g.A1) click in the cell and insert a number of your choice ~ now click in the next cell in the column (i.e. A2) and type =sum(A1+1) and hit Enter / Return. (or increment with whatever value you choose). There you go, all cells in that column will increment by your chosen value, as will subsequent submissions.
Hope that works for you. You may get other answers - good luck.