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The X, Y, and Z input amplifiers servo to control the emitter current of transistors according to the applied signals. The transistors Vbe varies logarithmically to the current and so the emitter of Q2 includes the sum of the X and Y logs. The Z signal log is provided at the Q4 base so the resultant Vbe at Q4 is Vbe1+Vbe2-Vbe3. The output stage servo's the Q4 current to form the anti-log, so the resulting function is XY/Z. The thermal and electrical matching of the transistors eliminates the effect of temperature variations.