mmHg, also known as millimeters of mercury, is the unit for recording blood pressure, which is also calculated using kilopascals of atmospheric pressure. Blood pressure refers to arterial blood pressure, which is the lateral pressure generated by the blood flowing in the arteries against the walls of the blood vessels, and is commonly measured by mercury sphygmomanometers, which are non-invasive, indirect methods of measurement. The earliest blood pressure measurements were made using atmospheric pressure and water column measurements, which measured large values and were influenced by many factors and were not easy to record, unlike mercury sphygmomanometers which take into account accuracy and portability. Eventually the World Health Organization unified with mmHg for blood pressure recording, even though there are still pneumatic and electronic blood pressure monitors, the final measured blood pressure values are converted to the commonly used mmHg, more convenient to record and communicate the condition. Normal adult blood pressure can be diagnosed as hypertension if it exceeds 140/90 mmHg and hypotension if it is lower than 90/60 mmHg.