Hi Eran,
Introscope is not really designed to display two metrics in this way. In general, the x-axis is time and the y-axis is the metric or metrics you are interested in. If you have a limited and small number of values for x, you could create a metric for each value of x and display the corresponding value of y at that time.
You can right-click on a graph in the investigator and export the data as a csv file so you could generate a combined x-y graph from the exports.
I hope that helps
Regards
Julian