An Engineering Touchstone to Enable Successful Designs

Successful systems are created by engineers who understand and design to the ultimate objectives of the project. When we lose sight of those objectives we start making design decisions based on the wrong criteria and thus create sub-optimal designs. Scope creep, group think, and simple convenience are frequent causes of this type of variation. An effective design assessment tool is a touchstone by which we can evaluate the effectiveness of ongoing design decisions and keep the focus on the optimal solution.


From ancient history, a touchstone is a tool for assessing the purity of precious metals. It has become a metaphor for evaluating the merits of a concept.

Engineers and others in the defense industry may be familiar with the Heilmeier Catechism1. This touchstone is a set of eight questions developed by former DARPA director George Heilmeier. They are still used by DARPA and many other organizations to evaluate proposed programs. They’re also a great tool for innovators to critically think through their proposals and develop their pitch.

Engineers need a similar touchstone to help focus, describe, and defend their design decisions. The Engineering Touchstone is a set of questions covering all relevant aspects of mission effectiveness. Depending on the scope of the decision, it can be used independently or as part of a larger decision package.

Tailoring of the question set is discouraged; instead, the engineer should tailor the amount of detail provided in each answer as appropriate for the intended audience.

Question Set

Note: All answers should be specific to the decision or design; general answers applicable to the whole system aren’t sufficient.

  1. What is the capability you are providing and/or challenge you are solving? (ConOps and OVs)
  2. Who will use/benefit from it? (Users and stakeholders)
  3. Where will they use it? (System and environmental context)
  4. When and why will they use it? (Mission context and use case)
  5. How will they use it? (Workflow and human interface)
  6. What is the maintenance and support concept?
  7. What are the constraints?
  8. What are the risks and uncertainties?

When to use the touchstone

The touchstone supports any significant design decision, whether it is an explicit decision such as a trade study or the decisions implicit in component design. It is equally applicable to hardware, software, and processes.

Program managers and engineering leaders can require their teams to use it when relevant. Even when not required, engineers may find it helpful to support their thinking, documentation, and presentations.

Depending on the type and scope of the decision, the touchstone can be used as a standalone tool or as part of a larger decision process. It is a useful tool to provide context for a trade study or decision matrix, ensuring that decisions aren’t being made in a vacuum. The touchstone focuses on mission effectiveness; other project considerations such as budget, schedule, life cycle cost, and producibility can be added as necessary.

Enabling system success

Effective engineering requires a solid understanding of the project goals. This understanding must be (1) shared among the team, (2) maintained consistently across the duration of the project, and (3) utilized for all design decisions.

This becomes harder as the project gets longer, larger, and more complex. Differing perspectives emerge among the team and decisions become influenced by less important criteria. Usually this happens so gradually that we don’t even notice until its too late.

Touchstones such as the one above solve this problem by making assumptions and criteria explicit. This builds and maintains shared understanding and provides a natural rubric by which to evaluate each decision.

What has been your experience with engineering touchstones? How would you improve it? What touchstones are valuable to you? Share it with the engineering community in the comment box below.


  1. Catechism really isn’t the best term, since it implies there are doctrinal answers. It’s also hard to pronounce. They’re often called the Heilmeier Questions instead.