You'd find less than 3 per cent in this sample from the air just above water surface.
Light coming in almost parallel to the water surface cannot pass through.
A safety stop of 1-3 minutes is made at 3-6 meters from the water surface.
A third of it (206 m3) lies above the water surface.
A rule change came in 1987, before the head had to be kept above the water surface during the entire stroke.
It would push the top of the box down to the water surface.
They are designed for children and adults to play on a water surface.
Each ring is claimed to last up to 30 days to control 100-square feet of water surface.
However, this was probably based on the assumption that the animals could not take off from the water surface.
This effect is seen only over a rippling water surface.
