What is conversion factor and PCU
The conversion factor specifies the price comparison unit (PCU) in relation to the item’s price unit and the number of price units contained within one price comparison unit.
The price comparison unit is linked to NOBB’s item group structure. Some item groups may have two PCU units.
Example:
Item group 1701060 — Stainless Steel Hexagon Screws A4 — has the PCU unit CEN (100 pcs).
Applies to the item with the item text: HEXAGON SCREW DG M6X40 A4 -50
This means there are 50 hexagon screws in one package.

On the screen, an example is shown where the price unit is PAK and the price comparison unit is CEN. The value 2 means you need 2 packages to make one CEN (100 pcs).

See how to calculate the conversion factor: How to Calculate Conversion Factors (PCU)
An overview of valid units and unit descriptions can be found here.