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about shocks, as in a research laboratory the instruments are subjected
to low variations of temperature and are not moved about much.
In manufacturing, the most adequate type is the automatic
monofunction instrument, which is very well-suited for these
conditions of use; it is moderately robust; its precision and its price are
limited.
Digital display instruments do very well for manufacturing;
– when the analog/digital conversion has been done, the displays
can, if needed, be situated at a distance;
– this type of display can be used unambiguously by anyone,
whereas reading a non-digital dial requires interpretation from the
operator;
– digital instruments can be equipped with thresholds to
automatically find out those results that do not fit in a given range;
– digital measuring makes it easier to pass the measurements to a
global control by computer.
Nevertheless, a digital instrument is not to be used when the
operator has to do an adjustment because then the display changes
constantly and the operator cannot read its variation, nor even which
way it varies.
For a building site, you have to choose instruments that are
automatic and multifunctional and the accuracy of which is limited;
however, they must be watertight and very robust.
For a metrology laboratory, monofunction instruments with high
accuracy and resolution will be preferred. Whenever you have to
make a choice, you should choose types without in-built references
and purchase separate references, for example:
– length comparators and separate gauges;
– Wheatstone’s bridges and separate electric resistances in order
to be able to use several references alternately, then you can go on
working while some references are left with a calibration laboratory.
Ease of calibration and verification should be taken into account.
If you have to choose between adjustable references and fixed
references, choose the latter because the traceability of a fixed element
is easier to establish; an adjustable element may have been modified
without it appearing in its file.

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