FYI –
Here’s another slight tweak – adding more useful short-cut buttons to ‘Add Single Marker’ and ‘Add Marker Pair’ – as those are more frequently used and would be useful to have directly accessible in the top-level UI; thus these new icons will directly add the corresponding marker/measurement, rather than opening up a side-bar view / list of existing elements already added.
If you think it is useful, you could also add one for Analyzer – but it wasn’t as straight forward, as there isn’t an existing ‘Add New Analyzer’ – you still need to select which one you want from a list (and that operation isn’t likely done as often as adding Timing Markers or Measurements).
Finally, depending on how the scrolling of the timeline might overlap/interfere with these buttons, they could be made ‘semi-transparent’ unless moused-over, or just just move them to the top 3 buttons on the side bar and visually ‘grouped’ together as a set of ‘add’ buttons under the Play/Start button above the other ‘menu’ buttons. Also, they could be moveable and/or hidden, so people to tweak the looks to their own taste (if you think it is worth the extra effort to do that – I’d rather have a horizontal cursor on the analog channels myself 
). Meanwhile, I do now think these could be a useful addition to the UI, and not redundant with the existing side bar menu.
I put icons in both places – just to visually prototype the idea:
