A quantitative value system (also known as a number-based value system) is one where value is measured exclusively by quantity - a number.  Because of this, such value systems inherit three core properties of numbers: they are limitless (conceptually, you can always add more value by increasing quantity), they are linear (a larger number is always worth more than a smaller number), and they are consistent (value comparisons and calculations are universal, based on simple math).

[Note that numerically measuring progress towards a fixed goal is not exactly a quantitative value system, because it embodies the concept of sufficiency, making the dichotomous goal (of having versus not-having) qualitative.]

Anything that can be counted could be thought of as the potential basis of a quantitative value system - the most common example being money, because it is also theoretically limitless.  Monetary (or virtual) wealth is also unique in that it can often be increased using pure math alone.

A key encapsulation of any quantitative value system is the idea that More is Always Better.  Contrast this with a qualitative value system.

source: Andrew Welch