Why does my chart have duplicate or missing signs on the outer circle of the wheel?
Astrology chart wheels are drawn in different styles. One of the most common styles in Modern Western Astrology, is to only draw the signs that are at the cusp (the beginning) of each house.
If a house is narrower than 30 degrees, often times a sign will be at the cusp of this house and also at the cusp of the following house, so it will be drawn twice. The sign is only once in the chart spanning 30 degrees, but we draw it once for each house cusp that it covers.
On the other hand, if a house is wider than 30 degrees, sometimes an entire sign is contained within that house and not drawn at all because it's not at the cusp of the house. This condition is called "intercepted sign." The sign is still there, we just don't draw it because it's not at the cusp of any house.