An altimeter measures height, read as awareness of how high you have risen or how far there is to fall. Tradition links it to ambition kept in check by caution.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.