I have seven number fields in my Responsive form and I would like to sum them in real time so the user can see the running total.  The total doesn't need to be written to the list, just shown on the form.

I've tried setting calculated column in Sharepoint, I've tried setting the default value of the "total" control to a formula of sum(column1,column2, column3) and I haven't been able to get it to work.  I'm sure this is simple and I'm just missing something.  Please help!