the step of issuing said alarm condition includes issuing a first said alarm condition indication when said distance error across hold by first position and a second said alarm condition when said transverse distance error exceeds threshold by second distance, which is said error greater than said first hand distance.
the step of issuing said alarm condition indication includes issuing a first said alarm condition indication when said transverse distance error exceeds said thresehold by a first distance and a second said alarm condition when said transverse distance error exceeds said threshold by a second distance, said second distance greater than said first distance.