The ActivityJobItems table is a table used in the Work Orders and Field Crew apps. Just like a transaction has a table to hold line items, a work order uses the ActivityJobItems table to hold line items.
This table has a Cost field that cannot be manually updated. It is a calculated field which uses other fields within the ActivityJobItems table.
How the Cost field is calculated
The calculation differs depending on the type of item:
For Service items:
Cost = CostPer & ActManHrs
For other item types:
Cast = CostPer * Qty