pro rdvelseq,rdformat,sequence,start,length,i1,i2,i3,i4,hdr

  len=abs(length)
  imno=indgen(len)+start
  if length lt 0 then begin
    aux=imno
    for i=0,len-1 do imno(i)=aux(3+8*(i/4)-i)
  endif
  imno=strtrim(string(imno),2)
  exlen=strlen(imno)
  exten=replicate('.0000',len)
  for i=0,len-1 do begin
    ext=exten(i)
    strput,ext,imno(i),5-exlen(i)
    exten(i)=ext
  endfor
  if strupcase(rdformat) eq 'F0' then begin
    fzrd,sequence+exten(0),i1,hdr
    fzrd,sequence+exten(1),i2
    fzrd,sequence+exten(2),i3
    fzrd,sequence+exten(3),i4
    if len eq 8 then begin
      fzrd,sequence+exten(4),aux & i4=i4+aux
      fzrd,sequence+exten(5),aux & i3=i3+aux
      fzrd,sequence+exten(6),aux & i2=i2+aux
      fzrd,sequence+exten(7),aux & i1=i1+aux
    endif
  endif else begin
    fitsrd,sequence+exten(0),i1,hdr
    fitsrd,sequence+exten(1),i2
    fitsrd,sequence+exten(2),i3
    fitsrd,sequence+exten(3),i4
    if len eq 8 then begin
      fitsrd,sequence+exten(4),aux & i4=i4+aux
      fitsrd,sequence+exten(5),aux & i3=i3+aux
      fitsrd,sequence+exten(6),aux & i2=i2+aux
      fitsrd,sequence+exten(7),aux & i1=i1+aux
    endif
  endelse

end