Setup
Write or find a paragraph of 60 to 120 words of plain declarative prose. Not poetry. A paragraph from something you wrote and abandoned is ideal, because you have no emotional stake left in it.
Set twelve minutes. Minutes 1 to 3: break it into lines for the first time, aiming for lines of about eight to ten words. Minutes 4 to 8: rewrite it from the unbroken paragraph as lines of four or five words. Minutes 9 to 12: one more pass, this time breaking only where the meaning turns, with no target length at all.
The one rule that matters
You may not add, remove, or reorder a single word. Punctuation may change; words may not. The moment you allow yourself a new word, you are not testing line breaks any more, you are rewriting, and rewriting is how you avoid the test.
Trim the paragraph to fit the shortest version before you start, not during. If a clause has to go, cut it in minute 0 and then use the shortened paragraph for all three passes.
Reading the three versions
The long-line version usually tells you what happened. The middle version usually tells you what it felt like. The short-line version usually tells you what the speaker noticed, one item at a time, and it is almost always the version with the most pressure in it — because five short lines have five opportunities to be a decision.
In the worked example, version three turns a travel problem into a list of humiliations: still / on the ramp / with both bags / and no ticket. The words are identical to version one. Only the last line being two words long gives the poem its ending.
What to do with the result
Keep the version you would not have written. That is the whole value: the drill exists to push you off your default line length, and your default is the one you produce without deciding anything.
Do not publish any of the three. Do it again next week with a different paragraph. After four or five runs, a preferred length starts to appear on its own, and you will be able to say why you chose it.