If our example resistor ended in gold (orange, white, black, gold), its 39 Ohms value could be five percent higher or lower. For a possible minimum of 37.05 or a maximum of 40.95.

A pull-up resistor connects your input directly to a positive voltage (5V or 3.3V). This keeps the input signal HIGH when the component is inactive, and switches it to LOW when you do trigger it.