= Biomedical engineer
A \b[biomedical engineer] develops, investigates or evaluates systems at the intersection of <engineering>, <biology> and <medicine>. Work can include instrument design, <biomechanics>, <biomaterials>, data analysis and technical support for medical equipment. The role includes constructing models and experiments, not only assembling a finished device.<Bioengineers and Biomedical Engineers by the U.S. Bureau of Labor Statistics>[What They Do, Duties and examples of technical specialties]{ref}
An original <load cell> example makes the measurement work concrete. Suppose reference loads $F=2\,\mathrm N$ and $6\,\mathrm N$ produce outputs $V=0.30\,\mathrm V$ and $0.70\,\mathrm V$. Fitting the stipulated linear <measurement model> $V=kF+b$ gives
$$
k=0.10\,\mathrm{V\,N^{-1}},\qquad b=0.10\,\mathrm V.
$$
A later output of $0.50\,\mathrm V$ then corresponds to $4\,\mathrm N$. Ignoring the offset would instead report $5\,\mathrm N$. With the calibration coefficients held fixed, an output uncertainty of $0.01\,\mathrm V$ contributes $0.10\,\mathrm N$ to force uncertainty; uncertainty in the reference loads and fitted coefficients adds further terms.
The engineer must also determine whether that model remains useful. A third reference load tests interpolation; repeated loading and unloading can reveal <hysteresis>; a temperature change can expose drift. Mounting the sensor on a biological specimen can alter the load path compared with the calibration fixture. Thus a satisfactory calibration curve is one part of demonstrating fitness for the intended measurement. Collaborating with users and reporting the conditions and limitations connects engineering performance to the biological question.
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