What a reference range is

[MOCK] This is placeholder text for lesson 2 of the Making sense of your labs track. Dr. Tagge will replace it with the real lesson. It stands in for the opening idea of the lesson, the part a reader sees before the email gate.

[MOCK] A second short paragraph goes here. In the real lesson it explains the idea in plain language, with one concrete example and the honest limit of what is known.