When you want to combine two Continuous fields, it is possible to create a Dual Axis. With a Dual Axis, there is one axis on the left, one on the right, and the Marks are superimposed. To create a Dual Axis, right-click on the second Continuous field and select Dual Axis, as shown in the following screenshot: 

When using Dual Axis, the pills are merged in the Rows or Columns shelves. If the Mark types are set to Automatic, they might change while using Dual Axis. However, it's still possible to edit them individually by using the different Marks shelves. By default, Tableau also puts Measure Names in Color to distinguish the two fields. You can modify Color or remove it.

With Dual Axis, the range of the two different axes can be different. For example, it's possible to compare the sales in dollars and discount in percentages. The two axes don't necessarily have the same range. However, if you're comparing values with a similar scale (such as the sales of the current year and the sales of the last year), the axes need to be in the same range. To do that, right-click on an axis and select Synchronize Axis.

What if you need to compare more than two Measures? To do that, you'll use Measure Names and Measure Values.