I'm reading Mary Oliver's 'A Poetry Handbook'. As part of doing so, marginalia (making notes in the margin) is a practice by some readers that I'm finding very helpful. There are many new-to-me words that definitions on the same page are very useful to have (e.g. prosody, enjambment). Then there is her chapter about metrical lines that is a whole new world to me, although master poets and/or writers may view it as common knowledge. Using marginalia is also providing me the opportunity to make related observations based on my experience as a former musician. In music, a learner is taught that there is a specific number of beats in each measure based on a time signature. That is what I find resonating for me as I read about the metrical line of prose that Ms. Oliver writes about. She presents a very nice legend of metrical lines in poetry (five-foot, four-foot, three-foot, etc.), their names (pentameter, tetrameter, trimeter, respectively and etc...