Similar story, not mine: TV repairmen back in the day would have frequent in-home callbacks, with the TV owner stating the TV picture wasn’t as good as before the repair.

So, after a repair the repairman would adjust the v-hold so the image would slowly rotate. “Tell me if the picture is getting better or worse.” If it was getting worse, they’d flip it back the other way until the customer was satisfied they were seeing the best picture.

Apparently cut callbacks to near zero.