SUM on MOD

Help Please......

I have 10 assets that I plan maintenance for. Each planned maintenance exam has a +/- 2 day tolerance. Each asset runs in order from 1 to 10 then over again (every 10 days).

I need a column that will calculate how many days above or below its actual completion date was compared to its planned completion date.

I assume it will be a combination of IF, SUM and MOD, but have spent a while trying to figure something out without much success yet.

Attached is an example spreadsheet with a column providing the expected result.

I cannot understand how you are getting some of these results. Please see the red numbers and explain how you got them.
Data Range

Date	Planned	Actual	Expected Result
1-Jan-20	1	1	0
2-Jan-20	2	2	0
3-Jan-20	3	3	0
4-Jan-20	4	5	+1
5-Jan-20	5	6	+2
6-Jan-20	6	7	+3
7-Jan-20	7	5	-2
8-Jan-20	8	7	-1
9-Jan-20	9	1	+2
10-Jan-20	10	3	+3

In your new sample, explain the last two rows.

Here's how I see it:

Most of the results can be calculated as =D7-C7
The row 15 and 16 results can be calculated as =MOD(D16-C16,10). This formula also works for many of the others, but fails for others.
The real question I see is how to decide when to apply the MOD() function and when not to. Once we know that, we can use an IF() function -- =IF(condition,MOD(D7-C7,10),D7-C7)

How do you choose? How did you decide that row 13 (planned 7 actual 5) was 2 days before and not 8 days after? How did you decide that row 16 (planned 10 actual 3) is 3 days after and not 7 days before?