A large central gauge, shown here, displays what the car's electric motor is doing, moment by moment. Outside is a tachometer that shows how fast the motor is spinning. It goes below zero because sometimes the motor acts as a generator. Driven by a device in the car's brakes, the motor can spin backwards, producing electricity that is sent back to the batteries.
The circle in the center indicates how much hydrogen is being used. When no hydrogen is being consumed, the circle is small and blue. As more hydrogen is flowing to the fuel cell, the ball grows in size and changes from blue to green to orange to yellow.
The blue shading to the right of the "hydrogen ball" indicates how much hydrogen is left in the tank.