When you refer to a summary field in a calculation, the summary evaluates as though you are using the summary field placed in a grand summary, header or footer layout part. You get the grand total, not the sub total shown in a sub summary layout part.
To get the subtotal, use the GetSummary Function to return the same subtotal that your summary field displays in each sub summary layout part. The "break" field that you use as the second parameter in the getSummary function should be the same "when sorted by" field that you selected for the sub summary layout part.
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