;+
;PROCEDURE:  timespan, t1, dt
;PURPOSE:
;  Define a time span for the "tplot" routine.
;INPUTS:
;    t1:  starting time (seconds since 1970 or string)
;    dt:  duration of time span  (DAYS is default)
;KEYWORDS:   set one of the following:
;  SECONDS
;  MINUTES
;  HOURS
;  DAYS     (default)
;
;CREATED BY:	Davin Larson
;LAST MODIFICATION:	@(#)timespan.pro	1.14 97/06/04
;-
pro timespan,t1,dt,  $
  SECONDS = seconds,      $
  MINUTES = minutes,      $
  HOURS = hours,          $
  DAYS  = days,      $
  CURRENT = current

@tplot_com.pro
if keyword_set(current) then begin
   t1 = systime(1)
   dt = -abs(current)
endif

if size(/type,t1) eq 0 then begin
   t1 = ''
   read,t1,prompt='Start time  (format: yy-mm-dd/hh:mm:ss)? '
   dt = 0.d
   time_units=''
   read,dt,prompt='Duration (# of days)? '
   days = 1
endif
if n_elements(t1) eq 2 then begin
  tr = time_double(t1)
endif else begin
  start_time = time_double(t1)
  if n_elements(dt) ne 0 then begin
    case 1 of
      keyword_set(days):    deltat = dt * 86400.
      keyword_set(hours):   deltat = dt * 3600.
      keyword_set(minutes): deltat = dt * 60.
      keyword_set(seconds): deltat = dt
      else:                 deltat = dt * 86400.
    endcase
  endif else deltat = 86400.
  tr = minmax([start_time,start_time+deltat])
endelse
dprint,dlevel=2,'Time range set from ',time_string(tr[0]),' to ',time_string(tr[1])
str_element,tplot_vars,'options.trange_full',tr,/add_replace
str_element,tplot_vars,'settings.trange_cur',tr,/add_replace
str_element,tplot_vars,'options.trange',tr,/add_replace
str = time_string(tr[0])
refdate = strmid(str[0],0,strpos(str[0],'/'))
str_element,tplot_vars,'options.refdate',refdate,/add_replace

return
end