i have data that is
2002/03/04 12:00:00 +1
2002/03/04 13:20:00 -1
2002/03/04 12:10:00 +1
2002/03/04 15:00:00 +1
2002/03/04 17:00:00 -1
but i should drawing like this..
2002/03/04 12:00:00 1
2002/03/04 12:10:00 2
2002/03/04 13:20:00 1
2002/03/04 15:00:00 2
2002/03/04 17:00:00 1