A column can be added to the Items Perspective that gives the sum of a numeric occurrence data field. 
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Set up
In order to view the sum of an occurrence numeric data field, it is important to associate a Data Type (unit of measurement).
A user with administration rights will have to create the field in the Item Occurrence GUI. 
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To view the value for a single occurrence, add the column via the column picker. 
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To view the sum total of the occurrences as a column in the item perspective, add the column via the column picker. 
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