1.  First look at File>System Configuration>System Settings and you will see that cost that is received into Stock.  This is either Standard (which uses the Standard Cost held against the Received Parent Item) or Average (which uses the Actual Cost of the Received Parent Item)

If using Standard Costing then the created Journal will comprise of   Cr WIP with Actual Cost  Dr Inventory at Standard  Dr Assembly Cost Variance (Actual Cost - Standard Cost)

If using Average Costing then the created Journal will comprise of   Cr WIP with Actual Cost  Dr Inventory with Actual Cost

2.  What determines the 'Actual Cost' of the Receipt?

Assembly Rule 'Default Receipt Cost Method' lets you define how Ostendo determines the Cost of the Received Parent Item.

 The Options are:
  - Standard:  The Standard Cost held against the Received Parent Item is used

  - Actual: The Actual Cost of the current WIP divided by the outstanding Quantity determines the 'Actual' Cost per Item

  - Planned: The sum of the 'Planned Costs' of the Components in the Order divided by the original Order Quantity determines the 'Actual' Cost per Item.

 Therefore what do we mean by the 'Planned' Cost?  If you go Assembly Rules you will see 'Planned Item Cost Method' and 'Planned Descriptor Cost Method'.  Ostendo determines the Planned Cost of the Assembly Order by multiplying the Component Usage in the Order by the Planned Cost method for each line and dividing the sum of the result by the Order Quantity.  This then becomes the Unit Cost of the Received Parent Item

3. Because the Assembly Receipt Cost may be different to the Value in WIP then any remaining Costs when the Assembly Order is 'Closed' will be posted to 'Job Cost Variance'