Standing waves also occur on electrical transmission lines. A line with a non-resistive termination will cause a reflection of the signal from the termination with the same amplitude as the incident wave. These waves will cancel periodically along the line causing nulls every half wavelength. The distance of the first null from the termination depends on the nature of the terminating impedance. Nulls on transmission lines are very sharp, in contrast to the peaks which are broad and flat. This makes the nulls easier to measure. An instrument in electronics for measuring the positions of nulls on a line is the slotted line. This instrument can also be used to measure VSWR. With the measurement of VSWR and the null positions the value of the terminating impedance's magnitude and phase can be calculated.