Question

how do we measure the amplitude of a wave? from top to top or bottom to bottom from the starting point to ending point of a wave from top to bottom from the resting position to top or resting position to bottom

Explanation:

The amplitude of a wave is defined as the maximum displacement of a particle from its resting position. So, to measure it, we consider the distance from the resting position to the top (crest) or from the resting position to the bottom (trough) of the wave.

Answer:

from the resting position to top or resting position to bottom