Well OK, let's take the Audacity measurement as "exact", I have a problem with what I would do, as a user of the App, to measure the shutter speeds if I don't have a clear method (such as: first peak to last peak, or base of first peak to base of last peak, etc.) and if I have to choose the measure extremes on the graph based on "circumstances".

Maybe, as the other site does, "base of first peak" to "base of last peak" should be easier to identify. It should always be the same method in any case or the user would end up just choosing the method that more easily matches the desired speed...