Poor Drafting Practices
I also got my drafting "education" as a machinist trying to read others' unintelligible scrawl. The ultimate question that any drawing should answer: "How would a complete stranger (with the proper skills) make this part?"
I have sent costumers into furious tizzies about "poor quality" because I gave them exactly what they asked for. One customer (a high end, "bold look" plumbing fixture company) rejected an entire shipment because the parts did not fit. I had called to warn that the parts don't fit together as drawn, and was summarily shooed away with a "you are only a machinist, do what we say". I made sure that 100% of those parts were within 1/3 of tolerance from nominal as specified on the print. Some of my best work ever. Did they learn? I did not stick around long enough to find out, since I graduated from college the following week :-)