plot two datasets after merge

Every minute, some data is collected at 2 computers:

COMPUTER1 COMPUTER2
UpdateTime Count UpdateTime Count
38:09.6 13,349,601 37:58.6 1,501,230
39:59.9 13,349,680 39:57.7 1,501,245
42:00.0 13,349,761 42:00.5 1,501,258

I want to compare ONLY the RATE at which Count is increasing. So:

step 1. Kinda Normalize data by subtracting each row from first row. so data looks like:

COMPUTER1 COMPUTER2
UpdateTime Count UpdateTime Count
38:09.6 0 37:58.6 0
39:59.9 79 39:57.7 15
42:00.0 160 42:00.5 28

step2. Merge datasets, but somehow keep each computer data separate

UpdateTime Count
-37:58.6 0
38:09.6 0
-39:57.7 15
39:59.9 79
42:00.0 160
-42:00.5 28

step3. Plot this on graph (Time on X, Count on Y), so that Computer1 is Blue and Computer2 is Red color.

How to do this simple way or any inbuilt mechanism etc.?

You can leave out step two. Using an XY chart, the data produced from step 1 can feed the chart. See attached.

Could you explain how to create this?

I tried 'scatter' plot but it doesn't show both Computers data.