Abstract: 4-component borehole strainmeter observes horizontal strain changes near the surface. However, direct readings of the instrument do not denote exactly the strain changes. In order to obtain the data that can be converted in accordance with strain theory, relative in-situ calibration should be done first, and then absolute in-situ calibration. Since strainmeter virtually measures changes in strain status, increments should be used in conversion. For precise studies, in-situ calibrations should be carried out corresponding to the concerning period of time. As an example, the data from Guza station are processed and the results given.

Key words: Borehole strainmeter, 4-component borehole strain observation, In-situ calibration, Earthquake precursor