There are many kinds of systems that can be analyzed both quantitatively and qualitatively. NTS resources are geographically restricted and both quantitatively and qualitatively limited. Thinking Quantitatively and Empirically, and Thinking Technologically and Digitally. Often, these variables are measured quantitatively. It must be noted that microscopy techniques may not yield quantitatively accurate results. Theoretical production ecology tries to quantitatively study the growth of crops. There two primary methods used to quantitatively understand resonance Raman enhancement. Clausius developed this in his efforts to explain entropy and define it quantitatively. There is no theoretical framework quantitatively describing the strength of such decoherence effects, though. In economics, contour lines can be used to describe features which vary quantitatively over space. Since 1991 it has decreased drastically in all regions, both quantitatively and proportionally. Early attempts to quantitatively describe the electromagnetic force were made in the mid-18th century. They can also quantitatively stabilize carbocations. A soluble base is called an alkali if it contains and releases OH ions quantitatively. PVC produces HCl upon combustion almost quantitatively related to its chlorine content.