Comparing values in one column for each unique value in another column

Hi all!

I often use this forum to find answers to questions I have, but I have been unable to find one, so here I am...posting for the first time.

I have three column. One is a time column, one is a system assigned ID column, and one is a user assigned ID column. The system assigns a new ID each time a new user is detected and that system ID is retained for each update (once per second) until the user is no longer detected. If a period of 30 seconds or more passes and the user returns, the system assigns them a new ID. I've found an issue where there are some false reports being generated. Basically here is what I want to do:

For each unique user assigned ID (this is always retained no matter what) I would like to examine the system assigned IDs and determine if, at some point in the file, user assigned ID is assigned a new system ID and then, later on, reverts back to the original system ID. Here is a super simplified example of what I'm dealing with:

Time System ID User ID
9:00:01 5 123
9:00:02 5 123
9:00:03 5 123
9:00:04 5 123
9:00:05 5 123
9:00:06 5 123
9:00:07 6 123
9:00:08 6 123
9:00:09 6 123
9:00:10 5 123
9:00:11 5 123
9:00:12 8 124
9:00:13 8 124
9:00:14 8 124
9:00:15 8 124
9:00:16 9 124
9:00:17 9 124
9:00:18 9 124
9:00:19 8 124
9:00:20 8 124


Basically I want to see, "hey! for user ID 123, the system ID changed from 5 to 6 and then back to 5. For user ID 124, the system ID changed from 8 to 9 and then back to 8).

Perhaps one way would be to, for each unique USER ID, highlight the rows in a different color for each unique system ID.

I know this is confusing. I am thoroughly confused and probably didn't do a good job explaining this.

Thanks for any help that anyone may be able to provide!

Assuming data in Col.A,B & C

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