An electrical probe is constructed of a small capacitor in contact with the circuit node under test so as not to
load this circuit node and cause distortion of the input signal. The small capacitor is then placed in series with the small
input resistance of a terminated coaxial signal line. The voltage signal at the output of the coaxial line will be approximately
the product of the small capacitance, the resistance of the coaxial line and the derivative with respect to time of the
input signal. Tungsten probe tips can be sharpened to 100nm or less, enabling measurements of nanoscale devices.