Update: a1=-1 is a bad choice of test value (0 is much better), as it won't show the issue if present! However, it doesn't change the outcome of the test on 060

Update: a1=-1 is a bad choice of test value (0 is much better), as it won't show the issue if present! However, it doesn't change the outcome of the test on 060, but I would have noticed that 020 is affected as well (as also mentioned in the comments to the article).