The discussion will be restricted to measurements of voltage and current. Also, although the measurements themselves should be as quantitative as possible, the discussion is rather nonquantitative. Emphasis is on types of instruments, how they may be used, and the inherent advantages and limitations of a given technique. A great deal of information can be obtained from good, clean voltage and current data. Power and impedance are obviously inherent if the proper time relationships are preserved. Often an associated, difficult-to-determine, physical event can be evaluated from the V-I data, such as a time-varying load characteristic, or the time of light emission, etc. The lack of active high voltage devices, such as 50-kV operational amplifiers, restricts measurement devices to passive elements, primarily R and C. There are a few more exotic techniques that are still passive in nature. There are several well-developed techniques for voltage measurements. These include: spark gaps; electrostatic meters; capacitive dividers; mixed RC dividers; and the electro-optic effect. Current is measured by either direct measurement of charge flow or by measuring the resulting magnetic field.