but I am not working with tables,
But you are working with a table. Without at least one table, you can't create records and enter data into your file. And you can link this table to itself in a relationship as a way to count related records. Open Manage | Database | Relationships. Find the Tutorial: What are Table Occurrences? box for the table that stores the data in your example. Use the mouse to drag from the ECR # field out away from the box and then back to the same exact field. FileMaker will ask you if you want to create a new occurrence (in FileMaker 13) or Instance (Older versions) of this table. Select Ok to do that. If your original table was named ECRData, this new occurrence of that table will be named ECRData 2. You can now define a calculation field in ECRData as Count ( ECRData 2::ECR#) and this field will show your count of all records in the table with the same ECR# value as that of the current record.
and when I try to use a Summary Field, (ECR # Count->Summary->Count of "ECR #") it counts every record that has a valid "ECR #" field.
Well it counts every record in your found set where ECR # is not empty. But in a list view layout, you can add a sub summary layout part "When sorted by ECR #" and put your summary field inside this sub summary layout part and it will count all the records with the same ECR # value in your current found set (rather than the whole table), but only if you sort your records on this ECR # field.This is called a Summary Report and you can set it up to list the individual records or just have one row for each unique value in your ECR# field. For more on summary reports, see: Creating Filemaker Pro summary reports--Tutorial