Even if modest compared with the formal uncertainty, there can be differences between measurements made using old and new instructions. How do I handle this at a job site?
Rather than risk the possibility of inconsistent measurements in the 1.5 to 2.5 mil overlap range (38 to 64 um) we recommend that jobs currently in progress be completed using the old instructions (i.e., no averaging). Inspectors will always have the option of continuing to use the old instructions wherever agreements between contracting party and inspector specify doing so or where a need for process consistency requires it, however we do recommend switching to the updated instructions at the start of subsequent new jobs IF BOTH INSPECTOR AND CONTRACTOR ARE COMFORTABLE MAKING THE SWITCH. Measurements made using the new POF-HT averaging procedure should be marked “HT”. Measurements made using the old (non-averaging) procedure should be marked “non-HT”.
