Howdy! can be replied to with just a nod and a smile. It simply means Hi! in Texan - not How are you doing?. Or you might reply, Hey Y'all Doon? if you want to engage in proper Texan interactions. Replying in proper English, well pronounced, with each syllable clearly spoken, is HIGHLY discouraged.
The crest of a wave is the point of maximum positive displacement, or upward movement, away from equilibrium, or an undisturbed state. The opposite of crest is trough, which is the point of the greatest negative, downward displacement.
The vertical distance between the wave crest and trough is the wave height. The amplitude of the wave is half of the wave height. The distance from a certain point on one crest or trough to the same point on the next crest or trough is the wavelength. The period is the amount of time it takes for succeeding crests to pass a specified point.