U-tube is just a glorified pendulum. But using this classical U shape for liquids is worth it. Pendulums is how you measure mass if gravity is too low.
I know some people inverted U-tube and immersed piezo fork into liquid. Then they struggled with reflections and setting feedback right or making sweep practical enough. And then there is electrical connections going into the probe through liquid surface, which is another concern. Still, in batch process (and all brewing is batch process) immersible probe should be much faster and washable than flow-through, I guess.
Ciders and cysers are perfect drinks for Gravmas celebration! Although myself I’m planning citrus melomel for the evening, brings up childhood memories. Tried to share photos of 3x decoction weisen from the eve, but lost fight to foam miserably, for it was not the first bottle for the evening.
My wife said that Christmas specials should be made on Christmas for the next one. Sounds legit. I think that’d be my plan for now.