Sorry, but "records in a field" makes no sense. Records are made up of fields. Fields do not contain records.
Do you want to count the number of records in a table where a specific field is not empty?
Do you want to count the number of records in a found set where a specific field is not empty?
Do you want to count the number of repetitions in a repeating field that are not empty?
Let me see if I can clear up what I mean.
I have 8000 members. I have the date of birth for all but 400. I need to get the total number of members that have dates. So I need to calculate the members with dates while excluding those without.
Hope this clears it up a bit.
That would be the total number of records in a table where a specified field is not empty.
There are multiple ways to get this value. What you want to do with this value after you get it will determine which option is best.
I'll list just two, but these are not the only methods:
1) enter find mode. Put an * in the date field. Perform the find. The number of records in your found set (shown in the status tool bar on the left) will be the number of records in your table where this field is not empty.
2) Go to Manage | Database | Fields. Add a new field to this field of type Summary. Set it to do a count of your date field. Click OK to leave Manage | Database and add this new field to a layout based on your members table. Show All Records and this field will show the count of all records where the Date field is not empty.