The Yff contact circle is the circumcircle of the Yff contact triangle. Its center has triangle center function
 |
(1)
|
which does not correspond to any Kimberling center.
Its radius is
 |
(2)
|
where
 |
(3)
|
Its circle function is
 |
(4)
|
which does not correspond to any Kimberling center.
Kimberling center 
lies on this circle.
The orthocenter of the Yff contact triangle is the Nagel point of the reference triangle.
