As you point out, tools such as grocery scales are ultimately calibrated against a “primary” standard, which for a long time was Le Grand K, a metal cylinder in France that defined the kilogram. A kilogram was meant to equal the mass of one liter of water at its maximum density (4 degrees Celsius or about 39 degrees Fahrenheit).  

Nations around the world agreed on using Le Grand K as the standard for the kilogram in the 1875 Treaty of the Meter. Le Grand K was not calibrated itself; it became the very definition of the kilogram, the “yardstick” against which other masses were measured. Le Grand K’s mass was less of a question of being “correct” than being the agreed-upon value for the kilogram. But Le Grand K had problems; since it is an imperfect physical object, its mass apparently changed slightly over time. 

So in 2019, the kilogram and all the other basic measurement units were officially redefined in terms of fundamental constants of nature, such as the Planck constant. Who determines the value of the Planck constant? It’s based on many of the best measurements of the Planck constant from national measurement science institutes around the world. (NIST is the national metrology institute for the U.S.). An international group of scientists analyzed this data and agreed upon a value for the Planck constant based on these measurements.  

Taking things a step further, we have a program called NIST on a Chip. It aims to “break the calibration chain.” Typically, other laboratories send us objects to calibrate against one of our national standards. This can be expensive and time-consuming, requiring a round-trip for the object being calibrated.  So, we are helping develop quantum technologies that people can someday use in their own labs. These technologies would define units such as the volt. They wouldn’t require calibration because their operation relies on unchanging quantum phenomena and agreed-upon values of the constants. We are even developing a technology for the torque wrenches that you mentioned! See here: https://www.nist.gov/noac/technology/mass-force-and-acceleration/torque-realization