14.3.2 Effective number of pathsSome “transit-time” ultrasonic installations, particularly if paths are crossed, may have several paths at effectively the same level or relatively close together. In such instances it may not be appropriate to use the total number of paths to determine the uncertainty in integration, due to the limited number of paths. Therefore, some professional judgement may be required in order to determine an effective number of paths. For example, if there are two operational paths in a cross-path system at the same elevation, the ffective number of paths would be one.