FAQ
What does QL-B1 mean on a utility drawing?
QL-B1 means a service was detected by two methods that agree, with position to ±150 mm and depth to ±15%.
QL-B1 is the highest detection quality level in PAS 128:2022 below exposing the service. Position and depth come from both methods, and they agree. Horizontal tolerance is ±150 mm and vertical is ±15% of depth.
QL-B2 is ±250 mm and ±40% of depth. QL-B3 is detected by one method with depth not reliable. QL-B4 is expected but not detected, so assume it is present unless excavation shows otherwise. A P after the level (QL-B1P) means the GPR data was post-processed in the office. See PAS 128 explained.
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