About your update. The two signals are totally unrelated. It just happens that the fan's noise seems to repeat at about 100 Hz, so giving about 1 pulse per half mains period. That they're unrelated can be seen from the fact that triggering on one signal, the other one won't remain in sync. The speed at which the second signal moves across the screen is determined by the frequency difference between both signals. It should be obvious that the fan's noise can't be in sync with the mains, since it's powered by a DC power supply which ideally has removed all reference to the 100 Hz at its input.    

What could be causing this sine on 7810 output when powering BLDC fan?
I have a settings view with a grouped table. One of the cells of such table is intended to show a very long list of items from where I want the user to select one. Due to the length of the list, I need to provide a way to make easier to find a certain item.

One of the options I think there are, is to show letters of alphabet as indexes at the right side of a plain table. Since my first table is a grouped one, my navigation hierarchy would be then like this:

  

Would it be inconsistent to navigate from a grouped table to a plain table? If so, could somebody give an existing example? I didn't find anything related to this in iOS Human Interface Guidelines, maybe it is described somewhere else and this navigation pattern breaks the guidelines.

Another option could be having a search bar. Can a search bar be used in both a plain table and a grouped table? The existing example of such bar I found is in Contacts app and it is a plain table. In a plain table, could both an alphabet index and a search bar be shown?
