When the tool tip touches the top of the tooth, the instrument signals that the apical foramen is reached.
[citation needed] It is unreliable though in the presence of fluid in the canal which requires additional drying.
[citation needed] The method of Kobayashi performs a calculation of the ratio of the measured impedance of two or more electric frequencies.
[citation needed] The Adaptive method of measurement is implemented by the so-called electronic apex locator.
In case of wet canal the device automatically adjusts the measurement method of Kobayashi.