That’s my point. Pressure based altitude is wholly unsuited for any type of absolute accuracy due to the inherent fluctuations.
Radar altimeters are one example of overcoming the limitations of pressure based instruments and trying to achieve 1cm of resolution when most are concerned with hundreds of feet being good enough, strikes me as trying to apply the wrong technology to the problem. As is typical around this forum, most of these question tend to have their origins in the x-y problem