It depends on your gauge length which I understand can vary between 50 mm to 2000 mm, but generally set to 200 mm (http://www.promat.hk/itm/495590/59044/Construction/NDT/Crack-Monitoring/DEMEC-strain-gauges-DEMEC-series?catspath=45387|46614|59044). Assuming it is 200 mm, a measurement of 0.001 mm will be equivalent to 0.005% strain or 0.05 milli-strain or 50 micro-strain. Hope this is of help.