Universal Principles of Design, Updated and Expanded Third Edition

188 Uncertainty Principle

Measuring things can change them, often making the results invalid.

The act of measuring sensitive variables in any system can alter them and confound the accuracy of the measurement. For example, a common method of measuring computer performance is event logging: Each event performed by the computer is recorded. Event logging increases the visibility of what the computer is doing and how it is performing, but it also consumes computing resources, which interferes with the performance being measured.1

The uncertainty introduced by a measure is a function of:

• Sensitivity of the variables — The ease with which a variable in a system is altered by the measure.
• Invasiveness of the measure — The amount of interference ...