It also displays original/final gravity, alcohol by volume (ABV), international bitterness units (IBU), and SRM (Standard Reference Method, a scale used to classify the color of beer in the USA. It is based on degrees Lovibond (degL) ).
Notice how many more Ales there are vs. Lagers? That's taste, my friend.
The T-shirt also sports degrees Plato:
[Wikipedia] The Balling scale was developed by German chemist Karl Balling. It refers to the concentration of dissolved solids (mostly sucrose) as the percentage sucrose at 17.5 °C. The Brix scale was originally derived when Adolf Ferdinand Wenceslaus Brix recalculated Balling's scale to a reference temperature of 15.5 °C. The Brix scale was subsequently recalculated again and now uses a reference temperature of 20 °C. Brix can be approximated as 261.3 × (1 − 1/g), where g is the specific gravity of the solution at 20 °C.
The Plato scale which measures in Plato degrees is also a refinement of the Balling scale. It uses a reference temperature of 17.5 °C and a slightly different modulus, with the approximation 260 × (1 − 1/g), where g is the specific gravity of the solution at 17.5 °C.
The three scales are often used interchangeably since the differences are minor.