Simplified Directional Facility (SDF) provides a final approach course similar to that of the ILS localizer although is not as precise as Localizer. It does not provide glide slope information. The SDF transmits signals within the range of 108.10 to 111.95 MHz. The approach techniques and procedures used in an SDF instrument approach are essentially the same as those employed in executing a standard localizer approach except the SDF course may not be aligned with the runway and the course may be wider, resulting in less precision. Usable off-course indications are limited to 35 degrees either side of the course centreline. Instrument indications received beyond 35 degrees should be disregarded. This angle is generally not more than 3 degrees. The SDF signal is fixed at either 6 degrees or 12 degrees as necessary to provide maximum flyability and optimum course quality.