Pinching like a pencil fixed my drift too... sore wrist though.

Wait, so the control line itself was good and you were just measuring off the slab edge instead? Because a 3/8 out of square slab doesn't really explain the bolts being off if you were pulling from a real control line. Sounds more like nobody set the line or showed you where it was, and Rick caught it after the fact. Handing a new guy the benchmark and control line on day one should be step one, not a lesson learned the hard way. That's on whoever ran the layout, not just you.

The "cleaning the fitting with steel wool first" part is the whole secret, I swear. I read somewhere that most solder joints fail because of oil or oxidation on the copper, not because of bad technique, and the flux alone won't cut through it. Did my share of cursing at leaky joints before I heard that, then felt pretty dumb after. My lottery win was replacing the flapper in the toilet tank, took five minutes and stopped a drip that had been running for months.