Abstract: Voltage control means output to a variable resistance part 2 a control voltage proportionate to an error between an input detection signal of an input terminal T.sub.i of a source follower field-effect transistor 1 and an output detection signal of an output-side transistor 5. Although said variable resistance part 2 changes its resistance value in accordance with a control voltage, a drain current flowing from the field-effect transistor to said variable resistance part is maintained constant by a constant-current source 3. Thus, an output voltage of the output side transistor changes in accordance with said error, thereby controlling the input detection voltage and the output detection voltage to be constantly the same.

Abstract: A method and apparatus used for determining phasing correlation between left-channel and right-channel signals of a stereophonic audio signal is provided. The determination of the phase correlation is facilitated by deriving centrally localized components contained in the audio signal to provide an indication representative of phase correlation existing between the left-channel and right-channel signals.

Abstract: A method and apparatus for calibrating the scale of an X-Y display device is provided wherein at least two intersecting linear loci are formed and displayed on the screen of the device to show the X and Y axes of effective coordinates of the display device. The display of intersecting loci facilitates adjustments of the device enabling effective coordinates to be coincided with the coordinates of the scale.