80% / cup

“The blind normally and merely use other senses to judge
the water level when they are filling the cup with water or beverage.
“80%” is a cup. It allows the blind to know the water level by touching it with thumb.
When “80%” is filled with approximately seventy to eighty percents of water,
the red buoy in the cup handle will rise.
Once the blind touch the buoy, they would stop filling the cup with water.