He then tells you to derate the window by a factor. This allows me to go to a 200 foot depth. He states that the factors used take into consideration arctic conditions and normal wear and tear on the windows. He also places a 10 year maximum life after which the window should be replaced. I also learned that you can not just cut a piece of plexiglass and insert it into the window mount etc.
Acrylic plastic is cast into sheets at the factory under heat and pressure.
This is the way that acrylic for windows is sold. If the designer simply cuts the plastic into the desired shape there are stresses set up at curing time that will cause crazing and possible failure of the window. For this reason the plastic must be heat treated. Two cycles of heat treating are required. First comes the shrink cycle.