* this fuction return the time difference between time1 and time2
      FUNCTION time_diff(time1,time2)
      IMPLICIT NONE

* input 
      CHARACTER*10 time1,time2

* output      
      REAL time_diff

* internal 
      INTEGER hr, min
      REAL sec, elapsed
      !REAL hr, min, sec, elapsed

      READ(time1(1:2),*)  hr
      READ(time1(3:4),*)  min
      READ(time1(5:10),*) sec

      !elapsed = 60.*(min + 60.*hr) + sec
      elapsed = FLOAT(60*(min + 60*hr)) + sec

      READ(time2(1:2),*)  hr
      READ(time2(3:4),*)  min
      READ(time2(5:10),*) sec

      !time_diff = 60.*(min + 60.*hr) + sec - elapsed
      time_diff = FLOAT(60*(min + 60*hr)) + sec - elapsed

      RETURN
      END