* Green: battery ok, i.e.: no water contained in the brake fluid
* Yellow: less than 1% of water content in brake fluid
* Yellow/yellow: approx. 2% of water content in brake fluid
* Yellow/yellow/red: approx. 3% water content in brake fluid
    the brake fluid should be changed
* Yellow/yellow/red/red: at least 4% of water content in brake
    fluid.the brake fluid must be changed urgently