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# 2.10.4.2 Easements with Fixed Sharpness

The values R, X and L are read-only. They are set using the radio buttons or the Value field which can be set to 0 (No Easment) or between 0.21 (sharpest Easement) 100 (broadest Easment).

These values indicate the worst case of joining a straight track with a curve of radius R. The two tracks are separated by the offset X while the easement curve extends for L/2 inches or centimeters to each side of the endpoints.

The formula used to draw non-Cornu easements is:

             x = l * l * l / (6 * R * L)
             r = L * R/l

where

- l is the distance along the tangent to the easement.
- R is the final radius of the easement.
- L is the total length of the easement along the tangent.
- x is the offset from the tangent at l.
- r is the radius of easement curve at l.

The Easement Button () on the Main Window (Section 3.1) changes its label to indicate the current easement value.

The following diagrams illustrates the R, X and L values and the resulting easement curve.

If curves with a radius larger than R or two curves (that bend in the same direction) are being connecting then the easement curve will be shorter and the offset smaller. If the computed offset is small then no easement is generated.

A curved track that bends in one direction and then bends in the opposite direction is an S-curve. This will generate the worst case easement which is two easement curves placed end to end.

Refer to instruction in section 2.10.4.3 when using sectional track.