Electrodes are the metal plates or nodes on a scale that make contact with your skin and conduct electricity through the body. They each transmit signals to one another, receive signals in return, and measure differences in voltage between two points of contact. The more points of contact there are, the more precise your results will be.
4-electrode scales typically come in the form of just footplate with no handle, have one electrode on each corner of the scale, and send signals only through the feet. Since these scales are confined to making contact through the lower body, they’re best for simply getting a general sense of what’s improved and what needs to change, beyond just your weight.
8-electrode scales typically come with a handle attached to the footplate, have four electrodes on the footplate and four on the handle, and send signals through the hands and feet. Because these scales have double the contact points and direct access to the upper body, they’re a better option for greater accuracy, deeper insights, and a more complete analysis.