The importance and value of manometry are presented with examples of patients in labour. It is important to distinguish between the pressures and the forces working on the fetus, especially as far as the causes of fetal bradycardia are concerned. Graphs of magnetic lag are shown in order to demonstrate that the tension on the fetus and sometimes on the placenta and the cord precedes and lasts longer than the increase in hydrostatic pressure which accompanies a contraction. The paper includes the following subjects: Introduction and general observations. The patient and the monitoring device and the tolerance to external and internal manometry by the patient. The concepts of pressure and force. The distrubution of pressures and forces in obstetrics. The measure of forces by their conversion into pressure in a manometric system. The interpretation of the results of the measure of pressure and force in obstetrics.