Humboldt H-4385 Resistivity Meter - Manual (Page 10)

4) Insert 4 new C-size alkaline batteries into each holder tube and reinstall the
tubes making sure that the battery polarity is correct (as labeled) in each
case.
5) Re-install the retaining clips.
6) Re-install the panel into its plastic case and re-install the 4 screws on the
front side of the panel.
With respect to calibration, it is recommended that the H-4385 be re-calibrated
on an annual basis.