These are lightweight 10MHz a.c. mains powered, dual trace instruments, with a single time base and two identical vertical amplifiers. The scanning area is 8x 10cm and has a time and voltage measurement accuracy of 5%. The use of solid state circuitry incorporating integrated circuits and field-effect transistors minimises drift and provides fast stabilization time. The facilities include a single trace display, or dual trace display with the two channels either chopped or alternated, and an external X mode. Type D1011 has the additional facilities of (a) x5 gain on each channel (b)switching one channel for true X—Y display, (c) algebraic addition of two input signals, (d) variable control of sweep speeds between the marked positions of the SECS/DIV switch. All references to the external operating controls are in capital letters e.g. BEAM FINDER. The standards used throughout for symbols and unit abbreviations are IEC27 and BS1991.