The Length drop-down list enables you to control the length of the flange and also can calculate the unbend lengh. Following are the options available in this drop-down list.

Inner	The unbend length of the flange is calculated from the inner face of the flange.
Outer	The unbend length of the flange is calculated from the outer face of the flange.
Exclude bend	The unbend length of the flange is calculated excluding the bend radius.
Bend line	The unbend length of the flange is calculated from the bend axis of the flange.
Inner tangent	Enables to calculate unbend length of the flange from the outer tangent. The blue lines represent the outer tangent length of the flange.
Outer tangent	Enables to calculate unbend length of the flange from the outer tangent. The red lines represents the outer tangent length of the flange, respectively.