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The Costs Types tab is used to define the various categories of field costs (i.e. equipment rental, specimen retrieval, etc.) - however you want to categorize your various field costs at a high level. Both a Name and Code can be defined an both are available in the Field Costs billing extract.
Cost Units
The Cost Units tab is used to define the various cost units used in field costs transactions (i.e. per trip, per test, per set, per sample, etc.). Some cost units can't be edited or deleted because MetaField depends on them for other purposes.