All measurements involve uncertainty.

Suppliers of measuring equipment usually specify the measurement uncertainty as a symmetrical interval around the measurement result:

Measurement result ± measurement uncertainty

Example: The length of a special measuring rod is 2000 mm ± 1 mm.

Variation can be positive in contexts like "varied workday," "varied training", etc.

For manufacturing companies variation can create headaches and huge cost.

When and how do you respond to a result?

Do you use facts or intuition? Do your customers decide when to react?

Or maybe you use statistical process control?

How do you react? Do you start looking for a special cause?