Following General Systems Performance Theory, the second major contribution toward achievement of Goal 1 (see Goals) was the introduction of the Elemental Resource Model (ERM) in 1987. It attempts to provide a complete (i.e., incorporating all human subsystems), quantitative franework for:

• describing the human system (at multiple hierarchical levels) and
• explaining the interface of the humans system to tasks.

The ERM is derived by applying GSPT and the concept of monadology to the human system. Monadology dates back to 384 B.C., but credit is given to Leibnitz for formalizing it and touting its importance. It is essentially the idea of using combinations of a finite set of "basic elements" to describe and understand something with a great deal of complexity; vis a vis chemistry, alphabets, genetic building blocks, etc. The concept is thus well accepted as being vital to systematic human system descriptions from certain perspectives (e.g., chemical, genetic, etc.). Success with the previous use of monadology, whether intentional or unwitting (i.e., discovered to be at play after a given taxonomy has emerged), compels its serious a priori consideration in pursuit of solutions to other problems.

Since resource economic principles and monadology are common to both chemistry and the ERM (via GSPT, in the case of the latter), it is useful to use think of the ERM as a "chemistry" for human performance. In fact, the extent of the analogy is quite striking (see Figure below) and, after careful thought, rather understandable given that the physical, tangible substances dealt with in chemistry are indeed the substrates of human performance. The ERM asserts, indirectly, that the field of human performance could benefit from having a table of basic elements of performance (and a means to define the elements) in the same fashion that the introduction of the periodic table of the elements gave birth to what we now consider to be the field of chemistry.

A summary of selected major aspects of the Elemental Resource Model (ERM) for human performance. The ERM provides a hierarchical, quantitative representation of the human system and tasks that humans execute (or wish to execute). It has many analogies to the science of chemistry and is useful to think of it as a "chemistry" for human performance.

As in chemistry, the ERM incorporates multiple hierarchical levels (basic element level, generic intermediate level, and "high" level). Performance resources at the "basic element level" are finite in number, as dictated by finite sets of human subsystems and their respective dimensions of performance. At higher levels, new "systems (e.g, "car polishers", "ball throwers", "car drivers") are readily created by reconfiguration of basic element level systems. Considering the human-task interface, success in a given task (which includes achievement of a given level of performance in a given type of task) requires that the inequality RA > RD is satisfied for each BEP involved. In other words, the human system must have "enough" of each performance resource. The threshold nature of the mathematics that describes this interface is particularly noteworthy.

Looking toward the human system, the entire human (lower right hand part of Figure) is modeled as a pool of elemental performance resources called Basic Elements of Performance (BEPs) and grouped into four different domains:

• life sustaining,
• environmental interface (containing sensory and sensorimotor subsystems),
• central processing, and
• information

Within the first three domains, physical subsystems referred to as functional units (defining grid columns in the Table of BEPs) are identified through application of fairly rigorous criteria. GSPT is applied to each functional unit, yielding a set of dimensions of performance (which define grid rows in Table of BEPs). A single BEP is defined by specifying: (1) the basic functional unit and (2) one of its dimensions of performance.

The domain containing informational elements is substantially different. Whereas the first three represent physical systems and their intangible performance resources, the information domain simply represents "information". Thus, memory functional units are located within the central processing domain, while the contents of memory (e.g., motor programs and associated reference information acquired through training or experience) are partitioned into the information domain. The overall approach permits even the most abstract items such as "motivation" and "confidence" to be considered with the same framework as strength and speed.