封底估算
封底估算即 Back-Of-The-Envelope Calculation。
\(1 天 = 24 hr \times 60 min \times 60 sec \approx 25 \times 4000 = 10^5 sec\)
\(1 生 \approx 1 世纪 = 100 yr \times 365 = 3 \times 10^4 day = 3 \times 10^9 sec\)
封底估算即 Back-Of-The-Envelope Calculation。
\(1 天 = 24 hr \times 60 min \times 60 sec \approx 25 \times 4000 = 10^5 sec\)
\(1 生 \approx 1 世纪 = 100 yr \times 365 = 3 \times 10^4 day = 3 \times 10^9 sec\)