Stethometer, in case, by Delolme, London.
A stethometer is used to measure how far the chest expands during breathing. The dial like device is placed on the front of the chest and the blue string stretched out to the centre of the back. When the patient breathes in, the movement of the string produces a reading on the meter. measurements from both sides of the chest can be taken and compared. These measurements are useful in diagnosing a disease such as tuberculosis, which in its advanced state can reduce how well a person is able to breathe.