The S43 and D43 are versatile oscilloscopes offering a wide range of facilities suitable for both general purpose and specialised application. This versatility is achieved by the use of separate plug-in amplifiers for the Vertical Deflection circuits and interchangeable time base/X amplifier units for the Horizontal Deflection Circuits. Simplicity of circuity and the "unit" method of construction make on extremely reliable Instrument which is easily maintained. Both the S43 and D43 use identical plug-in ampifiers and similar time base units, the only differences being the CRT circuit and the HT supplies. These are dealt with separately under the appropriate chapter headings.