If output impedance of a point is a high value then connecting another circuit at that point will load it, resulting in malfunction or error. Buffers are used as interface between circuits. Low impedance of an output means it can source/sink lot of current, when you need 2 opamps use LF353 or TL072 which are dual opamps.A non-inv FET input is the best buffer, for inverting buffer use high R values. Using very high R values like 2.2M or higher requires a glass epoxy PCB and guard rings around pin 2, 3 to prevent leakage currents on the PCB reaching the PINs. Also moisture and dust has to be prevented by using RTV coating or Varnish. Use 78L05 and 79L05 for the dual supply required by this circuit.
Buffer Unity Gain Op-Amp xml code
Vary the Millivolt Source by just hovering your Mouse pointer over the Two Buttons (Increment and Decrement). If you leave the mouse pointer on a button, the variation will pick up speed. Set a Value of your choice, positive or negative, you can set from -199.9mV to +199.9mV. Note the Output values on both the DVMs on the right (digital Volt Meter) in a Table. Repeat this for at-least 7 readings of both polarities. Jot the Formula below in your book and relate it to your table.