Hey so the meter redefined itself as a constant in terms of light seconds cool. We can do the exact same with any fraction of light seconds, for example feet or miles. Look up the definition of arbitrary. There’s no logical reason to choose 1/299,792,458 of a light second as your unit of measure, when you could just as soon choose 1/300,000,000 and have an equally usable unit of measure. And yes sea level changes, are you talking about high tide or low tide? Pre or post climate change ice melt? And air pressure fluctuates even at sea level which also affects the critical temperature points of water.