One particular problem I remember was a problem with flow for a machine tool hydraulic power unit. The flow was measured on a small flowmeter and was found to be 25% lower than expected. What ensued was an investigation into the system components. The pump was changed, the relief valve was changed and the motor speed was checked. This was not a great example of systematic fault finding.
Finally the calibration of the flowmeter was checked and found to be reading 25% lower. If your test equipment does not give the correct readings that makes testing and fault finding difficult. Couple this with a poor fault finding process and the time taken multiplies by a factor of 5.
