Use the radio buttons to select the number of sine waves added up. Each has a slightly different frequency.
When viewing a single sine wave, it's straightforward to measure its frequency, or wavelength. However, a question about its position is not so easy to answer. As you had more sine waves together, this changes. At n = 50, we can see where the wave has the largest amplitude, but it's now harder to describe its frequency in any meaningful way.
Link to stand-alone sim: Here is a link to view the sim on its own, with no distractions.