Physics: Physical measurement and calibration

Syllabus: PC_BK_05

This page covers terms like accuracy and precision, drift, hysteresis and calibration and has some videos on how you can explain this succinctly during a physics viva.


Accuracy: The ability of a measurement device to match the actual value of the quantity being measured.

Precision: The reproducibility of repeated measurements and a measure of their likely spread.

In the analogy of firing arrows at a target, the accuracy would represent how close the arrow was to the bullseye, whereas the precision would be a measure of how tightly packed together a cluster of arrows were once they had all been fired.

The Difference Between Accuracy and Precision in Scoping a Project

Drift: A fixed deviation from the true value at all points in the measured range.

Hysteresis: The phenomenon by which a measurement varies from the input value by different degrees depending on whether the input variable is increasing or decreasing in magnitude at that moment in time.

Non-linearity: The absence of a true linear relationship between the input value and the measured value.

What does this have to do with anaesthetics?

Accuracy and precision

Best examples for zeroing – arterial line. Removes a fixed drift and improves measuring system.

Good examples for calibration

Galvanic fuel cell: as these systems utilise a two-point calibration (gas containing zero oxygen, and one containing a fixed concentration), calibration drift occurs when protein and lipid deposits build up on the membrane or bubbles form in the electrolyte solution. To prevent this, a combination of regular electrode cleaning and quality control is necessary.

Blood sugar meter: There are two solutions of known glucose concentration, which give a high and low point for calibration.

Further reading:

Physics 4 FRCA

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