PROPOSAL: It is proposed that the name of this link be changed to UnitsLink, as this link type has nothing at all to do with quantities, and everything to do with units. Please recall that the normal definition of a quantity as a scalar value: the root-mean-square of a sine wave, the absolute value of a complex number, the length of an interval, the volume of some space, the length of a vector. All of thee quantities are normally unit-less: for example, what is the length of the complex number i? Its not feet or inches. How about the distance between the numbers 1 and 2? The volume of a unit cube? These are all quantities, none of them have units. By contrast, one can talk about a cubic yard of cement, a foot-long hotdog, the reactivity of a capacitor (complex number i, right there!!). These are physically meaningful, precisely because they have units. This link should be called UnitsLink and not QuantityLink.
QuantityLink <Unit> NumberNode n
10kg is represented by
QuantityLink ConceptNode "kilogram" NumberNode 10
1s is represented by
QuantityLink ConceptNode "second" NumberNode 1
$100 is represented by
QuantityLink ConceptNode "dollar" NumberNode 100