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Detail of the observation window.

The Project Mercury Familiarization Manual notes that the observation windows was located above the main instrument panel and consisted of an inner and an outer assembly. The inner window assembly was made up of three glass panes sealed in a titanium frame and attached to the cabin wall. The panes were independently sealed to provide a pressure seal between the panes. The outer window assembly consisted of a glass pane sealed in a titanium frame, attached to the capsule outer skin. The outer window assembly was sealed separately from the inner window assembly, to provide a complete seal. The outer window conformed to the curvature of the capsule conical section.