In medical practice, which instrument is specifically used to measure human blood pressure in millimetres of mercury?

Introduction / Context:
Blood pressure is one of the most important vital signs used to assess human health. Doctors, nurses and health workers measure blood pressure regularly to detect hypertension and other cardiovascular problems. Different instruments are used in medicine to measure various physiological parameters. This question asks you to identify the specific instrument used to measure blood pressure, so it checks basic awareness of medical equipment names.

Given Data / Assumptions:

- The parameter being measured is human blood pressure.
- The unit often used is millimetres of mercury, written as mmHg.
- Options include Sphygmomanometer, Thermometer, Electrocardiograph and Stethoscope.
- Only one of these instruments is designed primarily to measure blood pressure.

Concept / Approach:
A sphygmomanometer is the standard instrument for measuring arterial blood pressure. It usually consists of an inflatable cuff, a pressure gauge and often a stethoscope for manual measurement. A thermometer measures body temperature, an electrocardiograph records electrical activity of the heart, and a stethoscope amplifies body sounds like heartbeats and breath sounds, but none of these directly measure blood pressure by themselves. Recognising the function of each instrument makes it easy to choose the correct option.

Step-by-Step Solution:
Step 1: Read the question carefully and identify that the key task is measuring human blood pressure.Step 2: Recall that in clinics and hospitals, blood pressure is usually measured by wrapping a cuff around the arm and reading values from a gauge.Step 3: The combined cuff and pressure gauge system is known as a sphygmomanometer.Step 4: Thermometers are used for body temperature, electrocardiographs for heart electrical signals, and stethoscopes for auscultation of internal sounds.Step 5: Therefore the correct answer for the device that measures blood pressure is sphygmomanometer.

Verification / Alternative check:
If you picture a typical blood pressure measurement, you can imagine the cuff, the hand pump and the dial or digital display that shows two numbers like 120 and 80. That device is always called a sphygmomanometer in textbooks and exam syllabi. Most standard health education materials repeat this term, so if you have seen any chart of vital signs, this pairing is easy to confirm.

Why Other Options Are Wrong:
Thermometer: This instrument is designed to measure body temperature, not blood pressure. Common types include digital and mercury thermometers.
Electrocardiograph: This machine records the electrical activity of the heart and produces an ECG trace. It does not show blood pressure values directly.
Stethoscope: A stethoscope helps a doctor listen to heart and lung sounds and is often used along with a manual sphygmomanometer, but it is not itself a pressure measuring device.

Common Pitfalls:
Students sometimes confuse instruments because they are often used together. For example, when a doctor measures blood pressure manually, a stethoscope is used along with the sphygmomanometer. This can lead some learners to wrongly select stethoscope. To avoid such confusion, always link each instrument to the main quantity it measures. For blood pressure that key instrument name is sphygmomanometer.

Final Answer:
The instrument used to measure human blood pressure is the Sphygmomanometer.