Why is that when I introduce an ammeter or a voltmeter into a circuit, it alters it. In other words how does a *meter affect the circuit? I read somewhere that when you measure the resistance [using an ammeter], it is slightly different from the actual value. Why does this happen? And one more question. I did an experiment and they said that I should neglect the resistace of contacting leads used to hook up the circuit. That must mean that it could affect my results then. How so? --thank you.