计算从旧值到新值的百分比变化：
计算 新 value from 旧 value and percentage change:
从旧值 (V旧) 到新值 (V新) 的百分比变化等于新旧值的差除以旧值再乘以100%：
Price percentage increase from 旧 price of >Price percentage increase from 旧 price of 000 to 新 price of $1200 is caluclated by:
= 0.2 × 100% = 20%
Price percentage decrease from 旧 price of >Price percentage decrease from 旧 price of 000 to 新 price of $900 is caluclated by:
= -0.1 × 100% = -10%
The difference d is equal to the 旧 value V旧 乘以百分比变化 p 除以 100：
The 新 value V新 is equal to the 旧 value V旧 加上差值 d：
V新 = V旧 + d
