What can be done to reduce systematic errors during a measurement?
- Aadjusting the needle on a voltmeter so that it reads zero when there is no potential difference across it
- Bmeasuring the diameter of a wire at different points and taking the average
- Creducing the parallax effects by using a marker and a mirror when measuring the amplitude of oscillation of a pendulum
- Dtiming $20$ oscillations, rather than a single oscillation, when finding the period of a pendulum