Engineering Design GE121 Understanding the Clients Problem Part III

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Engineering DesignGE121Understanding the
Clients ProblemPart III

• Lecture 4A

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Measuring AchievementQuantifying What the Client
Gets

• Metrics are used to determine how well objectives
  have been attained
• Standards that measure the extent to which a
  design realizes our objectives
• Essential to selecting among design alternatives
  based on anything other than opinion and
  guesswork
• Often requires difficult choices
• What constitutes an appropriate metric
• How we can actually apply that metric
• How much it costs to measure

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Steps for Developing Metrics

• Identify units and scales for the thing to be
  measured
• Not heavy - weight or mass (kg? g?)
• Low cost currency (CAD, US ?)
• Temperature range military?, automotive?,
  commercial? climatic (specific to location?)?
• Identify means of assessing values of a design in
  terms of the units and scale selected
• Must ensure that it is compatible with units and
  scales selected previously
• Lab tests, field trials, consumer responses to
  surveys, focus groups etc.
• Estimating costs can be complex and demanding
  (More details in Chapter 8)

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Steps for Developing Metrics (continued)

• Evaluate whether or not the particular
  measurement is feasible and appropriate for the
  designs being considered
• Determine if the information obtained from the
  metric is worth the cost of obtaining it
• If its too costly
• find a new metric,
• find another means of measuring it,
• or look at other ways of assessing the design
• Use the cheapest alternative if more than one is
  available (assuming both have equivalent
  accuracy)
• May have to use a less accurate metric
• As a last resort, may have to treat it as a
  constraint with a go/no-go decision point

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Characteristics of Good Metrics

• Actually measures the objective
• Be sure that it REALLY is measuring what you
  intend
• Correct level of accuracy and tolerance
• Make sure its in the right ball park
• Repeatable
• Use a standard or document the procedure
• Understandable units of measure
• Furlongs/fortnight is not a good unit of measure
  for speed
• Use SI (metric) units unless the client specifies
  other units
• Unambiguous interpretation
• Must be clear to all members of the team as to
  what the results mean