Three parameters can be specified. All have a range from -1 to 1. Tension controls how sharply the curve bends at an input point. A value of -1 produices more slack in the curve. A value of 1 tightens the curve.
Continuity controls the continuity of the first derivative at input points.
Bias controls the direction os the curve at it passes through an input point. A value of -1 undershoots the point while a value of 1 overshoots the point. These three parameters give the user broad control over the shape of the interpolating spline. The original Kochanek paper describes the effects nicely and is recommened reading. Set the bias for all points.