Quantifying crustal rheology using rock samples requires good estimates of paleostress magnitudes. The inverse correlation between recrystallized grain size and differential stress, the “recrystallized grain size piezometer,” has been available since the 70’s as a means of estimating stress levels in quartz. Low confidence in the extrapolation from laboratory experiments to nature, however, hindered its widespread application. Using a combination of six independent estimates on crustal strength in Taiwan (see above diagram from my 2012 JGR paper), I have shown that under natural conditions the piezometer is actually quite accurate.