anchor.diff:        write(*,*)
        1 '-dy DY                 Increment in y direction (overrides -ny)'
         write(*,*)
  +     1 '-RX1/X2/Y1/Y2          Define limits with GMT limits format'
  +      write(*,*)
        1 '-z Z                   Third column (z) value'
         write(*,*)
        1 '-dip X0 Y0 Z0 STR DIP  Put grid onto plane with STR/DIP ',
  
positive.code:           p = 1
        elseif (tag(1:2).eq.'-h') then
            call usage(' ')
        else
            call usage('!! Error: no option '//tag)
        endif
  
negative.code:       endif
        write(*,*)
       1 'Usage: grid -x X1 X2 [-nx NX|-dx DX] ',
       2            '-y Y1 Y2 [-ny NY|-dy DY] -RX1/X2/Y1/Y2'
        write(*,*)
       1 '            [-z Z|-dip X0 Y0 Z0 STR ',
       2              'DIP|-xsec X0 Y0 AZ [-xz]]'
  