I have done a test with my boil kettle to try and determine the expansion and shrinkage rate. My kettle is a Big W 19.5l 310mm diam. I used a set amount of tap water being 15.75ls being 200mm in depth. This was taken to the boil and took another reading and got 16.14ls 205mm. The .005 difference is about .377ls. This is roughly 2.4% expansion. It was boiled for 60 mins where the evap was 50mm which is about 3.77ls leaving 12.37ls hot with a depth of 155mm. It was left to cool overnite as for no chill. The depth was 145mm cooled. This gave me a shrinkage rate of 4.8%. Are the expansion and shrinkage rates the same and does volume determine the expansion and shrinkage rate. These volume figures are worked out by 3.14x.0240(radius2)xdepths. Hopefully some can shed a little bit more light on this.