In court practice, the MCA criterion “to understand” was predominantly linked to either: (a) a relatively narrow, intellectual ability “to grasp information or concept,” or (b) a broader ability “to appreciate” or apply information to oneself. There were also links to an ability to imagine or abstract. In a small minority of cases, a “downstream” ability, e.g., to reason, was given as evidence for ability to understand.
Recommendation – “understanding” should be used only in its narrow sense of grasping relevant information or concepts. Such a narrow use of understanding would create more transparent and reliable judgments and communications. Applying information to oneself should be considered under “use or weigh”. See here for further discussion.