Goal: Create simple arithmetic that works for various digital times.

Usage: HH:MM format only, 12 or 24 hours.

Examples: Many examples are given below. Other examples exist.

0:00 works since 0+0=0, 0-0=0
0:01 works since 0/1=0
0:02 works since 0/2=0
0:03 works since 0/3=0
0:04 works since 0/4=0

0:05 works since 0/5=0
0:06 works since 0/6=0
0:07 works since 0/7=0
0:08 works since 0/8=0
0:09 works since 0/9=0

0:10 works since 0/1=0
0:11 works since 1-1=0
0:20 works since 0/2=0
0:22 works since 2-2=0
0:30 works since 0/3=0

0:33 works since 3-3=0
0:40 works since 0/4=0
0:44 works since 4-4=0
0:50 works since 0/5=0
0:55 works since 5-5=0

1:00 works since 0/1=0
1:01 works since 0+1=1
1:10 works since 0+1=1
1:11 works since 1/1=1
1:12 works since 2-1=1, 1+1=2

1:21 works since 2-1=1, 1+1=2
1:22 works since 2/2=1
1:23 works since 3-2=1, 1+2=3, 3-1=2
1:32 works since 3-2=1, 1+2=3, 3-1=2
1:33 works since 3/3=1

1:34 works since 4-3=1, 1+3=4, 4-1=3
1:43 works since 4-3=1, 1+3=4, 4-1=3
1:44 works since 4/4=1
1:45 works since 5-4=1, 1+4=5, 5-1=4
1:54 works since 5-4=1, 1+4=5, 5-1=4

1:55 works since 5/5=1
1:56 works since 6-5=1, 1+5=6, 6-1=5

2:00 works since 0/2=0
2:02 works since 2+0=2, 2-2=0, 2-0=2
2:11 works since 1+1=2, 2-1=1
2:20 works since 2+0=2, 2-2=0, 2-0=2

2:31 works since 2+1=3, 3-2=1, 3-1=2
2:42 works since 2+2=4, 4-2=2
2:53 works since 3+2=5, 5-3=2, 5-2=3

3:00 works since 0/3=0
3:03 works since 3+0=3, 3-3=0, 3-0=3
3:12 works since 2+1=3, 3-2=1, 3-1=2
3:21 works since 2+1=3, 3-2=1, 3-1=2

3:30 works since 3+0=3, 3-3=0, 3-0=3
3:41 works since 3+1=4, 4-3=1, 4-1=3
3:52 works since 3+2=5, 5-3=2, 5-2=3

4:00 works since 0/4=0
4:04 works since 4+0=4, 4-4=0, 4-0=4
4:13 works since 3+1=4, 4-3=1, 4-1=3
4:22 works since 2+2=4, 4-2=2

4:31 works since 3+1=4, 4-3=1, 4-1=3
4:40 works since 4+0=4, 4-4=0, 4-0=4
4:51 works since 4+1=5, 5-4=1, 5-1=4

5:00 works since 0/5=0
5:05 works since 5+0=5, 5-5=0, 5-0=5
5:14 works since 4+1=5, 5-4=1, 5-1=4
5:23 works since 3+2=5, 5-3=2, 5-2=3

5:32 works since 3+2=5, 5-3=2, 5-2=3
5:41 works since 4+1=5, 5-4=1, 5-1=4
5:50 works since 5+0=5, 5-5=0, 5-0=5

6:00 works since 0/6=0
6:06 works since 6+0=6, 6-6=0, 6-0=6
6:15 works since 5+1=6, 6-5=1, 6-1=5
6:24 works since 4+2=6, 6-4=2, 6-2=4

6:33 works since 3+3=6, 6-3=3
6:42 works since 4+2=6, 6-4=2, 6-2=4
6:51 works since 5+1=6, 6-5=1, 6-1=5

7:00 works since 0/7=0
7:07 works since 7+0=7, 7-7=0, 7-0=7
7:16 works since 6+1=7, 7-6=1, 7-1=6
7:25 works since 5+2=7, 7-5=2, 7-2=5

7:34 works since 4+3=7, 7-4=3, 7-3=4
7:43 works since 4+3=7, 7-4=3, 7-3=4
7:52 works since 5+2=7, 7-5=2, 7-2=5

8:00 works since 0/8=0, no remainder
8:08 works since 8/8=1, no remainder; 8+0=8
8:16 works since 16/8=2, no remainder
8:17 works since 7+1=8, 8-7=1, 8-1=7
8:24 works since 24/8=3, no remainder

8:26 works since 6+2=8, 8-6=2, 8-2=6
8:32 works since 32/8=4, no remainder
8:35 works since 5+3=8, 8-5=3, 8-3=5
8:40 works since 40/8=5, no remainder
8:44 works since 4+4=8, 8-4=4

8:48 works since 48/8=6, no remainder
8:53 works since 5+3=8, 8-5=3, 8-3=5
8:56 works since 56/8=7, no remainder

9:00 works since 0/9=0, no remainder
9:09 works since 9/9=1, no remainder; 9+0=9
9:18 works since 18/9=2, no remainder; 8+1=9
9:27 works since 27/9=3, no remainder; 7+2=9

9:36 works since 36/9=4, no remainder; 6+3=9
9:45 works since 45/9=5, no remainder; 5+4=9
9:54 works since 54/9=6, no remainder; 4+5=9

10:00 works since 0/10=0, no remainder
10:10 works since 10/10=1, no remainder
10:20 works since 20/10=2, no remainder

10:30 works since 30/10=3, no remainder
10:40 works since 40/10=4, no remainder
10:50 works since 50/10=5, no remainder

11:00 works since 0/11=0, no remainder
11:11 works since 11/11=1, no remainder
11:22 works since 22/11=2, no remainder

11:33 works since 33/11=3, no remainder
11:44 works since 44/11=4, no remainder
11:55 works since 55/11=5, no remainder

12:00 works since 0/12=0, no remainder
12:12 works since 12/12=1, no remainder
12:24 works since 24/12=2, no remainder
12:36 works since 36/12=3, no remainder
12:48 works since 48/12=4, no remainder

13:00 works since 0/13=0, no remainder
13:13 works since 13/13=1, no remainder
13:26 works since 26/13=2, no remainder
13:39 works since 39/13=3, no remainder
13:52 works since 52/13=4, no remainder

14:00 works since 0/14=0, no remainder
14:14 works since 14/14=1, no remainder
14:28 works since 28/14=2, no remainder
14:42 works since 42/14=3, no remainder
14:56 works since 56/14=4, no remainder

15:00 works since 0/15=0, no remainder
15:15 works since 15/15=1, no remainder
15:30 works since 30/15=2, no remainder
15:45 works since 45/15=3, no remainder

16:00 works since 0/16=0, no remainder
16:16 works since 16/16=1, no remainder
16:32 works since 32/16=2, no remainder
16:48 works since 48/16=3, no remainder

17:00 works since 0/17=0, no remainder
17:17 works since 17/17=1, no remainder
17:34 works since 34/17=2, no remainder
17:51 works since 51/17=3, no remainder

18:00 works since 0/18=0, no remainder
18:18 works since 18/18=1, no remainder
18:36 works since 36/18=2, no remainder
18:54 works since 54/18=3, no remainder

19:00 works since 0/19=0, no remainder
19:19 works since 19/19=1, no remainder
19:38 works since 38/19=2, no remainder
19:57 works since 57/19=3, no remainder

20:00 works since 0/20=0, no remainder
20:10 works since 20/10=2, no remainder
20:20 works since 20/20=1, no remainder
20:40 works since 40/20=2, no remainder

21:00 works since 0/21=0, no remainder
21:21 works since 21/21=1, no remainder
21:42 works since 42/21=2, no remainder

22:00 works since 0/22=0, no remainder
22:11 works since 22/11=2, no remainder
22:22 works since 22/22=1, no remainder
22:44 works since 44/22=2, no remainder

23:00 works since 0/23=0, no remainder
23:23 works since 23/23=1, no remainder
23:46 works since 46/23=2, no remainder

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Author: Eddie Maddox, USA, born 1955.
Website: http://EddieMaddox.com/
Copyright: https://creativecommons.org/publicdomain/zero/1.0/