The Preferred Unit of Measure is a Site wide setting (configured in the Site Manager > Catalog Configuration screen's General tab) which determines the default unit of measure to use for all Items.
Availble options for the Preferred Unit of Measure are:
When the Pricing Unit of Measure is selected, then the preferred unit of measure will be based on the unit used relative to base price returned from SYSPRO to CyberStore. This means that the Pricing Unit of Measure is either the Stocking, Alternate or Other unit based on how the Item is priced.
A unit of measure must be defined and visible for it to be used in CyberStore. A Stocking Unit of Measure is always defined, but the Alternate and Other units of measure are considered to be not defined when they have a factor of 0 or the same label as the Stocking unit.
A unit of measure is considered visible when the corresponding "Show" check box is checked in the Item Maintenance screen's Pricing tab.
If the Preferred Unit of Measure is neither visible nor defined, then it will fall back first to the Stocking unit, then to the Alternate and finally to the Other unit. If no unit is defined or visible, then any processes requiring a unit of measure will not be able to proceed.