Q: What is the difference between Shipment and Piece for dimensions, weight and volume?

A: ‘pieces’, ‘weight’ and volume under shipment are the total values for the shipment. Under Piece they are the values for a piece group.

For example you have a first piece group with 10 pieces, 10Kg, 1cbm and a second piece group with 5 pieces, 20Kg, 2cbm (so 2 objects in dimensions).
Then in the ‘pieces' under shipment you will have a total of 15 pieces, ‘weight’ (based on weight per piece) will be 200Kg and volume will be 3cbm.