This is the AWA version of the American RCA which was developed under the pressure of the First World War. Until this breakthrough in design, receivers needed two tall aerials making them an obvious target for artillery. For those early radios to select the required signal out from any competing noise, users needed to adjust them by turning the two selector dials, one with each hand. Advanced valve operation and a newly found method called reflexing, still in use now, to make a triode valve amplify while simultaneously perform two different tasks.  A powerful signal created by one valve was generated across a honeycomb coil called a harmoniser, allowing this internally generated continuous wave signal to be modulated by the amplified signal selected by the tuned aerial coil. Tuning required reference to two removable  cardboard charts inserted behind the pointer hands. In to order maintain the required difference frequency ( Harmoniser coil ') between the oscillator now  maintained in step (in harmony) with and the amplified distant signal. The resultant signal now remains just above the high end of the audible hearing range.