When we lived in Shrewsbury, we measured Summy's increasing height against a wall with pencil markings. We didn't disassemble that piece of wall to bring with us when we moved, though we would have liked to. So now there is no wall to measure against.
But Summy's found her own way - she stands against me or Kiran to see how much taller she's grown.
The other day, I was walking behind her on a path. In front of Summy was another little girl, carrying a skateboard under her arm. Summy quietly walked closer behind the girl, while measuring herself against the girl with her hand on top of her head. After deciding that the girl was probably about "the same tall as me", and hence, the same age, she caught up with her and made small talk.
Not that she would have not talked with an older kid. She loves older kids. And little toddlers. And babies. But especially kids who are the same size as her.