= Zero-setting device
A \b[zero-setting device] makes a <weighing scale> indicate zero with no load on its <load receptor>.<Non-automatic weighing instruments, Part 1>[OIML R76-1:2006(E), T.2.7.2, printed p11]{ref} A <tare device> instead establishes a zero indication with a load present. This difference identifies which physical reference the instrument is being asked to use.
For an illustrative linear response, write the unrounded mass indication as
$$
r(m)=am+b,
$$
where $m$ is the applied <mass>, $a$ is the response scale factor and $b$ is an additive offset. An ideal zero adjustment subtracts the unloaded indication $r(0)=b$, giving
$$
r_{\rm zero}(m)=r(m)-r(0)=am.
$$
If $a=1.01$ and $b=0.03\,\mathrm{kg}$, a true $1\,\mathrm{kg}$ load initially indicates $1.04\,\mathrm{kg}$ and indicates $1.01\,\mathrm{kg}$ after this zero adjustment. The $0.03\,\mathrm{kg}$ offset has disappeared, while the proportional <measurement error> remains. \b[Correct zero does not establish correct response at other loads]; a <calibration> using known nonzero loads tests that additional question.
A practical observation follows directly from the model: record the empty indication, apply a known load, remove it and check the empty indication again. Agreement at zero tests the reference return, while agreement under load also tests the response away from zero. Instrument-specific zero-setting limits still govern actual operation; the algebra describes an ideal offset correction rather than a replacement for those limits.
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