A Circle divided in Gon or Grads = 400 units

This measuring is about angular measurement.
In most places in the modern world a circle is divided into 360 degrees
and angles are measured in units of 1/360 of a circle = 1 degree
and degrees are divided into 60 minutes and for a finer measure minutes are divided into 60 seconds.
All this 360 - 60 and 60 measurement comes top us from the Babylonians.
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Shortly before the French Revolution the crown decided to have a single rational measurement system to be used throughout the France.
The scientific minds of the day decided to use a fraction of the circumference of the Earth as the base measurement.
The French Revolution happened, and the revolutionary government decided to continue to support the measurement system
and after much work the Meter was defined.
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The book The Measure of All Things - the Seven-Year Odyssey and Hidden Error that transformed the world
by Alder, Ken pub by - Free Press (Simon and Schuster), NY, 2002, is a great read explaining all this.
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The meter, defining linear measurement, was subdivided into decimal units (centimeters - millimeters) and expanded by decimal units (decimeters - kilometers).
The revolutionary government went further to decimalize the measurement of time and even proposed a decimalized calendar
though that did not last very long. It was too radical

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The decimalization of angular measurement was acomplished by dividing a circle into 400 units.
That measure being called a gon or grad .
I have not been able to find a visual representation for such a measurement, so I present one here.
Note that the definition of a gon is the equivalent of .9 (nine tenths) of a degree.