Abstract:The practice of continuously monitoring ground stress with the purpose to forecast earthquakes in China was initially led by Li Siguang. The early observation using piezomagnetic sensors attempted to measure stress directly. It had a basic disagreement in design from the viewpoint of elastic theory: piezomagnetic sensors measure force but displacement. Revolution took place both in theory and practice in 1977, which had paved the way for the socalled 4component borehole strainmeter to take over. However, mistakes have happened from time to time about this type of observation during the whole progress. The saying that stress can not be measured is groundless.