First of all, it seems this is automotive specific, so this particular forum is probably incorrectly placed.
Secondly, it would be helpful if you would put the year, make, and model in your post.
I agree with Mr. Hill. I'm not understanding the question either. What is the course you are referring to? Is the "needle" you are referring to the spike at the beginning of the traces? If so, I wouldn't worry about it. That is just probably noise.
I would caution you to use scope traces to determine if a catalyst is doing its job. You can have pre and post catalyst lambda sensors that appear to be mirroring each other and the catalyst is just fine. Trust the ECU to make that determination.
If you know the lambda sensors are active, you have checked for any TSBs for a reflash, and there are no exhaust leaks, then the only thing left is a new catalyst. You should be very careful if you choose to use an aftermarket catalyst. Their emission reduction efficiency will not be as good as OEM.