Final answer:
The amplitude of a waveform is typically measured in meters (m), but in electrical contexts, it can be measured in volts or millivolts (V or mV). Depending on whether the measurement is of an electrical signal or physical wave displacement, both voltage and amplitude in length units can be correct.
Step-by-step explanation:
The unit of measurement for the size or amplitude of a waveform is typically expressed in meters (m) in the International System of Units (SI). The amplitude is defined as the maximum displacement of the wave from its equilibrium (rest) position. In the context of electrical signals, amplitude can also be measured in terms of voltage (V or mV for millivolts), especially when analyzing alternating current (AC) waveforms in circuits. However, when specifically asked about the physical size of a waveform, it is represented in units of length such as meters. Regarding the choices provided in the question, option 3 which suggests both Voltage (mV) and Amplitude (mm) can be considered correct, depending on the context of the waveform's measurement - electrical signal amplitude can be in mV, while physical wave displacement might be in mm.