This is a Multisim Live graph showing the input and output of the op-amp, Vin and Vout, as recorded respectively by the blue and green voltage probes in Figure 37. The blue wave is the same as the one shown in Figure 38. It approximates a square wave and has a very small amplitude, oscillating around zero volts. The green (amplified) wave has a much greater amplitude. It approximates a rectangular wave, having small wiggles on the top and bottom where it should be flat.