function ssw_deltat, t0, t1, $
   seconds=seconds, minutes=minutes, hours=hours, days=days, loud=loud, $
   reference=reference


case n_params() of 
   0: message,"Need input timess..."
   1: times=t0
   2: times=[anytim(t0(0)),anytim(t1(0))]
   else:
endcase

case 1 of
   keyword_set(seconds): factor=1.
   keyword_set(minutes): factor=1./60.
   keyword_set(hours): factor=1./(60.*60.)
   keyword_set(days): factor=1./(60.*60.*24)
   else: factor=1.0
endcase

case 1 of
  keyword_set(reference): $
       deltat=( anytim(times,/tai) - anytim(reference,/tai) )*factor
  else:deltat=deriv_arr(anytim(times,/tai))*factor
endcase

if n_elements(deltat) eq 1 then deltat=deltat(0)
return,deltat
end