To dream of a diagram represents feelings about needing to explain yourself or explain a situation. It may even reflect needing to show others why something is or isn’t working the way it’s supposed to work. Carefully going over details about how something should function in your head.
Negatively, a diagram in a dream may be a sign that you are having issues speaking up when something in your life isn’t functioning the way it’s supposed to. Feeling that something isn’t right and being passive about it.
Example: A woman dreamed of a man making of a broken arm which he recognizes as her broken arm. In waking life the woman had a broken arm that was misdiagnosed as a sprain and didn’t feel that the doctors listened to her about it until the condition of her arm worsened