Anyway, there aren't an rules to limit your selection of numbers.
The U Factor ratings for windows run from .20 through 1.20 along with the lower the U Factor the better. Now that I have given you this over view working with the genuine article. http://krasathlet.ru/go/aHR0cHM6Ly9iaXRtZW1ldGFsay5uZXQvaW5kZXgucGhwP3RvcGljPTEwODExNzAuMA/YSU1QiU1RD1mYWNlYm9vaytvZitzZXgrJTI4JTNDYStocmVmJTNEaHR0cCUzQSUyRiUyRmtiYmw5Y196eF9ydzJfYy05cncuM3Bjby5vdXJ3ZWJwaWN2aXAuY29tTW9yZ2FuODIzJTQwd3d3LnRlbGVjb20udXUucnUlMkYlM0ZhJTI1NUIlMjU1RCUzRCUyNTNDYSUyQmhyZWYlMjUzRGh0dHBzJTI1M0ElMjUyRiUyNTJGd3d3LmZhY2Vib29rb2ZzZXgueWFmb3JpYS5jb20lMjUzRW5ldyUyQmNyYWlnc2xpc3QlMkJwZXJzb25hbHMlMkJhbHRlcm5hdGl2ZSUyNTNDJTI1MkZhJTI1M0UlMjUzQ21ldGElMkJodHRwLWVxdWl2JTI1M0RyZWZyZXNoJ