When you are designing analog circuits, you may find that you are always running to the parts bin for random resistors. It gets tiresome. And when you are biasing transistors, you would rather just wire it up and adjust for quiescent current than do all math first. It gets the job done faster. I found myself at this point alot lately. Solving equations for resistor values, then finding preferred values. Then picking out resistors from their bins and putting them into the breadboard. Take them out, replace with nearest value plus or minus. It was slowing me down, and a real inspiration killer. So I decided I should build a resistor substitution box.
