This new calculation feature in calculated form fields allows for summing up the total of a multi-entry number field across all entries.

For example, if you wanted to get the total “# of Fixtures” entered in a “Fixtures” multi-entry section, you could now add the multi-entry field "# of Fixtures" to a calculated number field by typing "@" and then searching for and choosing the desired form field in the search field that comes up. This calculation can be combined with existing calculations in the record type's Form settings.