Hertz measures cycles per second - one Hertz is one cycle per second. Unlike gauss that is a measurement unit for the strenght of a specific thing (an electromagnetic field), hertz is a generic frequency measurement.
Prepend is a word that means to attach content as a prefix. It is often used in different kinds of programming and in automated processes. Some prepending is done manually as a user. For example, a prepend command could be used in a scripting language that a programmer would enter into a certain function or code module. It would add certain characters of text to the beginning of some variable or object.
A preposition is a word that indicates location (in, near, beside) or some other relationship (about, after, besides) between a noun or pronoun and other parts of the sentence. A preposition isn't a preposition unless it goes with a related noun or pronoun, called the object of the preposition. Examples: Let's meet before noon. Before is a preposition; noon is its object. We've never met before. There is no object; before is an adverb modifying met. Rule 1.