Stadiometer: Wall Mounted Height Meter Growth Ruler CM Metric (Not Feet or Inches), 200 CM Range, Ideal for Clinics

um... how do i use it??? can someone attach picture of the setting?? I'm so confused...

Just received this and don't understand how to use it, seems like something is missing? like the meter that is placed on the head . . .

Does the measuring tongue stay in place so that a person could walk away and see their own measurement?