How do companies that make measuring tools like rulers make sure the product is accurate? Is there a universally ruler that is used to check? How do they make sure the measurements are exact?
In: Engineering
There **is** a standard bar that’s 1 meter long. It’s kept in Paris and high precision copies of it were distributed to government’s weights and measures departments around the world and from then copies were made and distributed internally to local offices and from there manufacturers bought copies for making and calibrating their own products.
The same goes for the kilogram.
These master copies are, presumably, extremely expensive as they are ultra high precision cut pieces of platinum, silver and palladium – intended to be as chemically inert as possible and fairly stable in length across a modest temperature range. These are a real “buy it for life” item.
Although the master copies are no longer technically the formal yardstick (literally), a while ago the meter was formally redefined as the distance light travels in a vacuum in a set time, because this is fixed and we can measure time more precisely than distance. The kilo has been/is in the process of being redefined also in terms of measurable fundamental units/properties, but that’s taken a bit longer to get to work/prove.
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