The EM161 module contains two electronic multiplying networks
 each of which needs an operational amplifier of the
DA163 module. The multiplier is a parabola multiplier  it
uses the identity (a+b)**2(ab)**4=4ab, so multiplying two
machine variables a and b is reduced to computing two times
a power of two function and subtracting the resulting values.
At the end of this operation the result is divided by four by
a resistive voltage divider and amplified by an operational
amplifier. The two parabola functions are generated by diode
function generators which approximate the desired parabola
function using secants.
