Switched from rule of thumb calculations to just taking a test shot at high ISO and zooming in on live view to check for trailing. That got me sharper stars in one night than weeks of math ever did. Works every time now and saves me from guessing.

Dakota, I secretly double checked once and found nothing, but that one time still haunts me.

You hit on something with that duct tape wallet. The fancier something looks the worse it usually works for actual use. I did the same thing with a waxed canvas apron. Looked great hanging on the peg board but the cheap cotton one from the hardware store has more pockets that actually hold tools in place. The expensive stuff is designed for people who want to look like they work instead of people who actually work.

Three times now, and I still catch myself doing it.

You ever mix pancake batter and think, "Yeah, this is the perfect thickness for my basement floor"? Because that's basically what I did. @west.claire you're dead on - that "frozen lake with bad bumps" is the best description I've heard. I swear the bag has fine print that says "may require a jackhammer and a therapist." Mine looked like a relief map of the Rockies after I was done.