Font weight in Firefox:

Font Weight in Chrome:

The font-weight value is of the order of 100 500 600 700 900, which is set in accordance with the W3C standard.
You can clearly see that the thickness of the text does not change linearly, and in another browser is not quite the same (it is almost the same from 100 to 500.). So, I wonder if there is a standard for how text is calculated according to font-weight ?
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