Help with Excel 2010: plotting graph 2 data sets where x axis sample points differ

I've searched around the net a fair bit and cannot find a way of doing this.
I'm generally OK with excel, but do find their graphs the most infuriating system out there. A gazillion options to make it pretty but nothing that helps you translate the data from tables to graphs :rolleyes:

My problem is this: I have two different sets of data I want to put on a single graph (they're dyno plots from my car). I've used some great open source tools like engauge and plotdigitizer to create data values from scanned print outs.

Unfortunately, the x axis (rpm) isn't to the same scale on both drawings, so I have data but where the sampling on the x axis differs, yet it relates to the same variable (rpm).

The only way I can think of doing it now it going over both graphs and picking out the same sample points on the x axis so that they "tie up" when brought into excel.

But surely there has to be a way of "merging" data on the same axis from two different data sets?

Any ideas?

OK, I've thought of a workaround: bring all the data into the same sheet then sort by rpm. I've now five columns: rpm, HP 1, torque 1, HP 2, torque 2 and have sorted by rpm. I now have one continuous increasing rpm range with the four data sets spread out across the rev range. Seems to work :)