A Quantity element is a type of Value element that carries a numerical value (such as a floating point or integer value) and can additionally carry a user-editable unit. Some quantities have a read-only (fixed) unit, which means the underlying value is used elsewhere in a calculation that assumes specific units.

The underlying value may be derived from other values or may be fixed as read-only (constant), in which cases the underlying value is not editable.

In the GreenDesk Expert System, the underlying value carried by value wrapper elements can also be 'null', which means "undefined" or "not known yet" and is then displayed as UNDEF. If you see a value element with an UNDEF symbol you usually need to "feed" the expert system with a value. Especially Activity pages, Credit pages, and Worksheet pages often prompt users for such values as needed.

Like most GreenDesk model element types, this element type has a dedicated web page that can also carry rich user notes and comments, and in some cases also file attachments. This element type can also be related to other model elements.

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