Be aware: These values are for the center of glass only. They should only be used to check the impact of various glazing styles, not to check whole window goods. Frame preference can drastically have an effect on efficiency. These values symbolize double glazing which has a 1/2″ air gap. https://mikemozart45789.wssblogs.com/36665780/the-smart-trick-of-secondary-glazing-london-that-no-one-is-discussing