SQL Server 2017

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CREATE TABLE #ResultsTable (
    Datum datetime,
    window char(10),
    countersOUT int,
    countersIN int,
    RESULT int)

insert into #ResultsTable values('20180104 08:30:00.000', '08:30', 0, 0, 0)
insert into #ResultsTable values('20180104 09:00:00.000', '09:00', 2, 1, 1)
insert into #ResultsTable values('20180104 09:30:00.000', '09:30', 1, 0, 2)
insert into #ResultsTable values('20180104 10:00:00.000', '10:00', 25, 9, 18)
insert into #ResultsTable values('20180104 10:30:00.000', '10:30', 45, 41, 22)
insert into #ResultsTable values('20180104 11:00:00.000', '11:00', 38, 37, 23)
insert into #ResultsTable values('20180104 11:30:00.000', '11:30', 50, 51, 22)
insert into #ResultsTable values('20180104 12:00:00.000', '12:00', 21, 24, 19)
insert into #ResultsTable values('20180104 12:30:00.000', '12:30', 12, 19, 12)
insert into #ResultsTable values('20180104 13:00:00.000', '13:00', 25, 18, 19)
insert into #ResultsTable values('20180104 13:30:00.000', '13:30', 35, 27, 27)
insert into #ResultsTable values('20180104 14:00:00.000', '14:00', 81, 9, 52)
insert into #ResultsTable values('20180104 14:30:00.000', '14:30', 113, 18, 70)
insert into #ResultsTable values('20180104 15:00:00.000', '15:00', 116, 34, 71)
insert into #ResultsTable values('20180104 15:30:00.000', '15:30', 123, 36, 54)
insert into #ResultsTable values('20180104 16:00:00.000', '16:00', 127, 35, 50)
insert into #ResultsTable values('20180104 16:30:00.000', '16:30', 103, 19, 47)
insert into #ResultsTable values('20180104 17:00:00.000', '17:00', 79, 31, 27)
insert into #ResultsTable values('20180104 17:30:00.000', '17:30', 50, 16, 26)
insert into #ResultsTable values('20180104 18:00:00.000', '18:00', 28, 11, 17)
insert into #ResultsTable values('20180104 18:30:00.000', '18:30', 16, 15, 2)
insert into #ResultsTable values('20180104 19:00:00.000', '19:00', 0, 2, 0)
insert into #ResultsTable values('20180104 19:30:00.000', '19:30', 0, 0, 0)
insert into #ResultsTable values('20180104 20:00:00.000', '20:00', 0, 0, 0)
insert into #ResultsTable values('20180104 20:30:00.000', '20:30', 0, 0, 0)
insert into #ResultsTable values('20180104 21:00:00.000', '21:00', 0, 0, 0)
insert into #ResultsTable values('20180104 21:30:00.000', '21:30', 0, 0, 0)
insert into #ResultsTable values('20180104 22:00:00.000', '22:00', 0, 0, 0)

select r.*,
       sum(countersout - countersin) over (order by datum) as result
from #ResultsTable r;

Datum	window	countersOUT	countersIN	RESULT	result
04/01/2018 08:30:00	08:30	0	0	0	0
04/01/2018 09:00:00	09:00	2	1	1	1
04/01/2018 09:30:00	09:30	1	0	2	2
04/01/2018 10:00:00	10:00	25	9	18	18
04/01/2018 10:30:00	10:30	45	41	22	22
04/01/2018 11:00:00	11:00	38	37	23	23
04/01/2018 11:30:00	11:30	50	51	22	22
04/01/2018 12:00:00	12:00	21	24	19	19
04/01/2018 12:30:00	12:30	12	19	12	12
04/01/2018 13:00:00	13:00	25	18	19	19
04/01/2018 13:30:00	13:30	35	27	27	27
04/01/2018 14:00:00	14:00	81	9	52	99
04/01/2018 14:30:00	14:30	113	18	70	194
04/01/2018 15:00:00	15:00	116	34	71	276
04/01/2018 15:30:00	15:30	123	36	54	363
04/01/2018 16:00:00	16:00	127	35	50	455
04/01/2018 16:30:00	16:30	103	19	47	539
04/01/2018 17:00:00	17:00	79	31	27	587
04/01/2018 17:30:00	17:30	50	16	26	621
04/01/2018 18:00:00	18:00	28	11	17	638
04/01/2018 18:30:00	18:30	16	15	2	639
04/01/2018 19:00:00	19:00	0	2	0	637
04/01/2018 19:30:00	19:30	0	0	0	637
04/01/2018 20:00:00	20:00	0	0	0	637
04/01/2018 20:30:00	20:30	0	0	0	637
04/01/2018 21:00:00	21:00	0	0	0	637
04/01/2018 21:30:00	21:30	0	0	0	637
04/01/2018 22:00:00	22:00	0	0	0	637