The liquidity estimation of order books in trading markets has always been an interesting topic. Recently, I came across a thought process where someone surprisingly referenced the logic used by the ancient Greek mathematician Eratosthenes over 2000 years ago to deduce the Earth's circumference based on the angle of sunlight. This approach is indeed brilliant—abstracting complex market depth data into a geometric problem, using minimal observation points to infer the overall scale. It sounds incredible, but this is the charm of interdisciplinary innovation. True breakthroughs often do not come from conventional solutions within a field, but from borrowing validated methodologies from completely different perspectives. Market analysis is no different—those with keen observation skills can find answers in history, in nature, and everywhere else.