# how would I calibrate a scale to 1 kilogram using the planck constant if I had nothing else to use?

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I read an article about tying the weight of a kilogram to the planck constant rather than Big K. I understand in principle using a mathematical equation to define the kilo using what we believe to be an unchanging constant force, as opposed to a man made object that will decay, or lose weight over time. What I don’t get is how I would use that equation to then calibrate an actual scale, or guage the weight of an actual physical object if all I have is the equation.

In: Technology Do you want a physicist solution or an engineering solution?

The physicist solution is that you take the planck constant and known physical properties of solid material and then scale up. You would need to make a separate device capable of extremely accurate time and area measurement, and then rederive it.

The engineering solution is that you use a liter of water to tare it. If you were capable of a measurement more accurate than that then you wouldn’t be in this situation. You don’t. Unless you’re trying to do ultra precise measurements your scale’s margin of error is by many orders of magnitude greater than the precision that the new measurement gives you. Scientists designed a scale that used the relationship between electromagnetic force and gravity to calculate Plancks constant, based on a weight calibrated against the Big K. They fixed that constant based on the kilogram. Having used the scale to get the constant, they can now use the same scales and the Official Planck constant to weigh things. The scale design is easily replicable. [Here’s a homemakeable version](https://www.youtube.com/watch?v=ewQkE8t0xgQ).

TL;DR: You build one of [these](http://aapt.scitation.org/doi/pdf/10.1119/1.4929898?class=pdf) out of Legos, and weigh whatever amuses you.