Spent three weeks un-cupping a wet oak slab and it finally paid off

I got burned almost the same way with a walnut slab I bought from a sawmill guy two winters back. The ends were checked and gray like it had been sitting forever, but the middle was still basicly fresh. My table top ended up with a twist you could see from across the room. Learned my lesson about trusting the outside of a thick board. What worked for me was similar to what you're doing, but I went slower. I skipped the fan becuase my garage gets down in the 30s overnight and I was worried about the surface drying faster than the core again. Just stickers and weight, and I let it sit for a couple months. The meter readings crept down slowly but they stayed even across the whole face, which mattered more to me than speed.

One thing I do now with anything over about 8/4 thick is drill a small test hole in the back edge with a Forstner bit, deep enough to reach the middle, and take the reading inside there before I buy. The seller hated it, so I either walk or pay accordingly. Hasn't steered me wrong yet. Glad the fan and weight are pulling yours back flat, and the breadboard glue-up should go fine once it's settled.

For what it's worth, I stopped trusting pin meters on thick slabs altogether. Mine only reads the top inch or so of the wood, so even when I poked the middle of a 3 inch ash slab it was mostly telling me about the surface. That slab read fine and still moved like crazy after I built the top. Now I just assume any thick slab needs a month or two sitting in my shop before I touch it with a jointer, no matter what the seller claims or what the meter says. The other thing that changed my life was designing for movement instead of fighting it. My last desktop got elongated screw holes in the aprons and the breadboard ends are pinned thru slots, not glued across the full width. When the wood swelled that winter it just slid instead of tearing itself apart.

I also started asking sellers if I can bring my own meter and drill a couple of shallow holes in the waste area near the center. Anyone who hesitates on that is telling you something. The guy I buy from now acutally keeps a cutoff from each log and lets me test that instead, which is a nice middle ground. Losing the Thanksgiving deadline stings, but a top that stays flat for ten years is worth one missed dinner.

I'd push back on the idea that a pin meter is useless on a thick slab. Mine came with longer snap-on pins, and if I seat them fully they read a good bit deeper than just the surface. Even the short pins are still useful for tracking trends over time, which is really what the Sunday check-ins are for anyway. I'm not saying the numbers are gospel on a 3 inch blank, but going back to guessing by feel seems like throwing out a tool that got you most of the way there. Did you ever try measuring both faces and averaging, or just pitch the whole method?

Reading this with some anxiety since I just picked up my first slab ever a few weeks ago, a maple one for a floating mantel. Thinner than what you guys are dealing with so maybe I'll be okay, but I haven't touched it with a plane yet and now I'm second guessing that plan. Stacked some scrap on top of it like you described just in case. One thing I can't figure out from searching though, when you check it every Sunday do you need to pull the weights off and let the wood sit bare for a bit before the reading means anything? My meter numbers seem to bounce around depending on where the stack is and I can't tell if that's the wood or just me doing it wrong.

One thing to watch when you re-glue those breadboards: even after the meter says it's even across the face, give it another couple weeks before the final milling. I flattened a sycamore top too soon once, readings looked good, and it still crept back a hair over the next month. Had to run it across the jointer a second time and lose a full 1/8 inch of thickness getting it flat again. These days I let a problem slab sit dead flat with weight for a solid month after the readings settle, then do all my final surfacing in one session right before glue-up. Also worth asking the seller to split a few dollars off next time, worst he can say is no.