A Sphygmomanometer, also known as a blood pressure monitor , or blood pressure gauge , is a device thatis used to measure blood pressure from aninflatable cuff is made and then released under the cuff in a controlled manner,  and a mercury or aneroid manometer to measure pressure. A manual sphygmomanometer with a stethoscope is used when using the oscillatory technique. A sphygmomanometer consists of an inflatable cuff, a measuring unit ( mercury manometer, or aneroid gauge ), and a mechanism for inflation which may be a manually operated bulb and valve or an electrically operated pump.
Both manual and digital meters are currently employed, with distinct trade-offs in accuracy versus convenience.
A stethoscope requires auscultation (see below). Manual meters are best used by trained practitioners, and, while it is possible to obtain a basic reading only through palpation , it produces only systolic pressure.
- The Mercury sphygmomanometer is considered the gold standard . They indicate pressure with a column of mercury, which does not require re-calibration.  Because of their accuracy, they are often used in clinical trials of drugs and in the clinical evaluation of high-risk patients, including pregnant women. A frequently used wall-mounted mercury sphygmomanometer is also known as a baumannometer . 
- Aneroid sphygmomanometers (the mechanical type with a dial) are in common use; Unlike mercury manometers, they may require a calibration probe. Aneroid sphygmomanometer is considered safer than mercury sphygmomanometer, although cheaper ones are less accurate.  A major reason for the departure from calibration is mechanical hassle. Arrowheads mounted on walls or stands are not susceptible to this particular problem.
Digital meters use oscillometric measurements and electronic calculations instead of oscillations . They can use manual or automatic inflation, but both types are electronic, easy to operate without training, and can be used in noisy environments. They measure systolic and diastolic pressures by oscillometric detection , employing either differential membranes that are measured using differential capacitance, or differential piezoresistance, and include a microprocessor .  They measure average blood pressure and pulse rate, while systolic and diastolic pressures are obtained less accurately than manual meters, And calibration is also a concern.    Digital oscillometric monitors may not be recommended for some patients, such as those with arteriosclerosis , arrhythmias , preeclampsia , pulsus alternation and pulsus paradoxus , as their calculations may not be accurate for these conditions. ,   And in these cases, an analog sphygmomanometer is preferable when used by a trained person.
Digital devices may use cuffs placed around the upper arm, wrist, or finger in the opposite order of accuracy  and portability and convenience.  Recently, a group of researchers at Michigan State University developed a smartphone-based device that uses oscillometry to estimate blood pressure.   The oscillometric method used gives a blood pressure reading that differs from that determined by auscultation, and varies according to several factors, such as pulse pressure , heart rate , and arterial stiffness , However some devices are claimed to measure arterial stiffness as well, and some can detect irregular heartbeats.
In humans, the cuff is typically placed smoothly and comfortably around the upper arm, approximately at the same vertical height as the heart, while the subject is seated with the arm supported. Other sites of placement depend on the species and may include a flipper or tail. It is essential that the correct size of the cuff is chosen for the patient. Too small a cuff causes too much pressure, while a cuff that’s too large causes too little pressure. For clinical measurements it is common to measure and record both arms at the initial consultation to determine if the pressure is significantly higher in one arm than the other. A difference of 10 mm Hg may indicate coarctation of the aorta. If the arms read differently, the hand with the higher reading will be used to read later. [ citation needed ]The cuff is inflated until the artery is completely occluded.
With a manual instrument, by listening to the brachial artery with a stethoscope, the examiner slowly releases pressure into the cuff at a rate of about 2 mm per heartbeat. As the pressure in the cuff drops, a “hushing” or loud sound is heard (see Korotkoff sounds) when blood flow first resumes in the artery. The pressure at which this sound started is recorded and recorded as systolic blood pressure. The pressure of the cuff is released until a sound is heard. This is recorded as diastolic blood pressure. In noisy environments where auscultation is impossible (such as the scenes often encountered in emergency medicine), the systolic blood pressure alone can be read (felt) by releasing the pressure until the radial pulse is felt. In veterinary medicine, auscultation is rarely used,
Digital devices use a cuff which, according to the device, can be placed around the upper arm, wrist, or a finger, in all cases to the same height as the heart. They inflate the cuff and gradually reduce the pressure, like a manual meter, and measure blood pressure by the oscillometric method.
While releasing the air pressure with the control valve, by looking at the mercury, or aneroid gauge pointer, in the column, the operator notes the blood pressure values in mm Hg. The maximum pressure in the arteries during the cardiac cycle is the systolic pressure, and the lowest pressure (in the resting phase of the cardiac cycle) is the diastolic pressure. A stethoscope, which is placed lightly over the artery being measured, is used in the oscillatory method. Systolic pressure (stage I) is identified with the first of the continuous Korotkoff sounds. Diastolic pressure is identified at the moment when Korotkoff’s voice disappears (fifth stage).
Blood pressure measurement is used in the diagnosis and treatment of high blood pressure (hypertension) and in many other health care scenarios.
The sphygmomanometer was invented by Samuel Siegfried Karl Ritter von Bach in the year 1881.  Scipione Riva-Rocchi introduced a more readily used version in 1896. In 1901, leading neurosurgeon Dr. Harvey Cushing offered an example of Riva-Rocki’s device. America modernized it and popularized it within the medical community. Further improvements were made in 1905 when Russian physician Nikolai Korotkov included diastolic blood pressure measurements after the discovery of “Korotkoff sounds”. William A. Baum invented the Baumometer brand in 1916,  while working for The Life Extension Institute, which performed physical insurance and employment.  The first fully automatic oscillometric blood pressure cuff was invented by Donald Nunn in 1981.
Word – medium
Word sphygmomanometer in conjunction with the sphygmo- + sphygmomanometer . The roots involved are as follows: Greek μός sphygmos “ pulse”, as well as the scientific term manometer (from French manometre ), i.e. “pressure meter”, itself coined from μανός manos “ thin, sparse” and μέτρον metron “measure”.   
Most sphygmomanometers were mechanical gauges with dial faces, or mercury columns, throughout much of the 20th century. Since the advent of electronic medical devices, names such as “meter” and “monitor” may also apply, as devices can automatically monitor blood pressure on an ongoing basis.