Using calculation fields in report writer

We've had some queries recently on using calculation fields in report writer; here's an explanation of how to do it.

When using merge-store to generate a report from a datafile, any fields in the report form must be written in terms of fields that exist in the datafile.

Calculation fields are not stored in datafiles. Even if a datafile is created using a form containing a calcuation field, that field name will not be recognised by the report writer - it needs to be defined in full in terms of the other fields it depends on. For example, you can define field suma=a1+a2 in the report form, provided that a1 and a2 are in the datafile.

You can also use calculation fields that depend on other calculation fields in a report, provided that all of them are defined in full. For example, define the fields suma=a1+a2, sumb=b1+b2 and sumtotal=suma+sumb. The field sumtotal will be interpreted correctly, providing a1, a2, b1 and b2 all exist in the datafile.

If you do not want the intermediate calculation fields to show up in the report, simply define them as hidden fields in the report form.

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