Glass hydrometer made in Australia by Carlton.
The oldest scale, Balling, was developed in 1843 by Bohemian scientist Karl Joseph Napoleon Balling (1805-1868) as well as Simon Ack. In the 1850s German engineer-mathematician Adolf Ferdinand Wenceslaus Brix (1798-1870) corrected some of the calculation errors in the Balling scale and introduced the Brix scale. In the early 1900s German chemist Fritz Plato (1858-1938) and his collaborators made further improvements, introducing the Plato scale. Essentially they are the same; the tables differ in their conversion from weight percentage to specific gravity in the fifth and sixth decimal places.
A rough conversion between Brix, degrees Plato or degrees Balling and specific gravity can be made by dividing the number behind the decimal point in the SG (which is often referred to as gravity points) by 4. So a specific gravity of 1.048 has 48 gravity points. 48 divided by 4 is 12 degrees Plato, Balling or Brix. This conversion method is accurate up to a specific gravity of 1.070 at which point the approximation begins to deviate from the actual conversion.
Winemakers, as well as the sugar and juice industry, typically use degrees Brix. British and continental European beer brewers generally use degrees Plato. American brewers use a mixture of degrees Balling, degrees Plato and specific gravity. Home wine, mead, cider, and beer makers typically use specific gravity.