# File lib/image_formats/D81.rb, line 50
def get_sector(track_no,sector_no)    
    return nil  unless track_no.between?(1,end_track)
                return nil unless sector_no.between?(0,D81_SECTORS_PER_TRACK-1)   
    track_start=D81_BYTES_PER_SECTOR*(D81_SECTORS_PER_TRACK*(track_no-1))
    sector_start=track_start+(D81_BYTES_PER_SECTOR*sector_no)
#    puts "T %0d, S %0d, TRACK OFFSET=$%x, SECTOR OFFSET=$%x" % [track_no,sector_no,track_start,sector_start]

                file_bytes[sector_start,D81_BYTES_PER_SECTOR]
end