If an operator excavates only 25 anomalies--of which 20 are within tolerance of 10% NWT--then the best estimate of the accuracy is [+ or -] 10% NWT 80% of the time, which is indicated by the location of the peak in Figure 6.
If the operator has little or no confidence in the sizing accuracy of the ILI tool, as may have been the case with older technology, then the operator might want to systematically excavate all indications after every ILI run.
If the operator were to excavate and examine each of these anomalies, it would expect that 80 anomalies would have a true depth between 25% NWT and 45% NWT.
The result is that with less accurate data the operator tends to excavate more anomalies to account for ILI uncertainty.
With a tool accuracy of [+ or -] 10% NWT 65% of the time, the operator would need to excavate all anomalies with a reported depth deeper than 55% NWT.
On one hand, highly accurate ILI data allows the operator to excavate fewer anomalies because of the confidence in the assessed severity.