yes this was in the hands on plastic weld samples and we had to go by part B specifications.  Well, the question was about undercut and undercut is undercut in my book and i was never told not to measure undercut in an underfilled joint so i did and i probably got that question wrong.  I totally see where your coming from about the undercut being caused by the underfill.  Undercut in a fillet weld is nothing but not enough weld metal in the joint.  So how is a guy thats never inspected before suppose to know not to measure a big ol chunk of undercut caused by an arc gouge in an underfilled spot.  The undercut went clear outside of the bevel so it was easily measured and really not part of the underfill in my book, but who's book do ya go buy?  I didn't have the guy that made the test teaching us how to measure his plastic weld samples.  Those samples probably had 12 CWI's sitting around them saying i see a 1/64" of undercut and the next guys says but my gauge is splitting the 1/64 and 1/32 mark and the last guy says well i'm seeing a 1/32 on my guage.  So then they flip a quarter and say we'll call it a 64th.  Who knows maybe these samples where measured with that new laser inspection to get the answer right on the money. Then you got lil ol me comeing along and using an undercut gauge totally unaccurate compared to a laser and i'm spliting the 1/64 and 1/32 mark and i guess wrong.  Don't know if i did, but i'm just saying i had to guess with your answers being A 1/64   B1/32   C 1/16   D no undercut.  You sit there and wonder if you have enough time to go up and down the whole seam on both sides every mm checking to make sure there is not one clear spot that has 1/32 so ya do anyway and all u find is where it splits the line, but ya still second guess yourself wondering if you accidently skipped over the one little spot.  Just a few of those second guessing yourself questions wondering what the guy got that made the test and your allowed 13 wrong so hopefully i'm in the ballpark.