The gap between the main arch and the matching arch of the control room, very light gray, can be easily seen in this head on view of the south/observatory end of the enclosure. The gap as drawn above is roughly 3.5" on both sides, for a control room arch diameter 7" smaller than the inside of the arch. The outside diameter of the main arch is 228" in diameter with an inner diameter of 222". The control room is therefore an outside diameter of 215". The telescope is pointing directly at the viewer.
 
 

This is a vew from the opposite end, facing south, looking at the north end of the enclosure. The narrow, medium gray path coming off the central back door of the control room is a sidewalk. The door opening is 32" wide and 80" tall, a standard door opening specification.