The rectangular metal can on the left, behind the decimal position select wheel, is the delay line memory.  Basically, a set of audio-frequency pulses are sent through a long metal coil over and over again.  The pulses coming out are fed back into the input, thus creating a serial memory.  Underneath the chassis and covering the entire bottom of the calculator is the main electronic circuit board, covered wall-to-wall with hundreds of early integrated circuit logic gates which form the calculator's "brain".  On the left is the power supply, and on the right is the CRT display tube.  Digits are formed by circuits which scan the electron beam to draw vectors, just like writing on an  etch-a-sketch.