The European Union has a regulation that requires EVs to illuminate their brake lights anytime the regenerative-braking system’s deceleration rate exceeds 1.3 meters per second squared, or about 0.13 g.
I quickly learned to force the break lights and started to follow this issue closely. That's how I became aware of the number.
How the EU saddled for 1.3 and not 1.2 or 1.4 is beyond my knowledge.