Shrinkage Rates vs Percentages

As felters we all know that felt shrinks as it fulls, but the age old discussion is how to measure that shrinkage.  I often hear felters talking about shrinkage in percentage values ie “It shrank by 30%.”  but this is an inaccurate and mathematically incorrect way of measuring shrinkage.  This series of video explains why, and how to calculate the most accurate method.