The following code may actually work. I haven't tried it yet.
The problem I think I may run into is that it is based on half the distance, in pixels, of the parent <div> (divwidth/2).
And I dont think this is the actual center date of the timeline. And it has other issues like when a window is re-sized.
It becomes even more problematic when you have 3 different timelines stacked on top of each other in a browser window.
We have written a timeline operating system that allows you to place an unlimited number of synchronously scrolling timelines in a single browser window. Although placing more than 4 timelines in one window, that scroll, center date, with each other, seriously degrades the browsers
performance (Chrome is the best performer here).
With the following code, their (width/2) may not correspond to the exact same date/time.
I dont really care whether the lines exactly line up, visually, vertically. What I do want is that if I have 3 timelines stacked on top of each other. And I scroll timeline #1's vertical line to say Dec 2, 1941, the other timelines (#2 and #3) will have their vertical line scroll to the exact date of the Pearl Harbor attack, so I can see, with all accuracy, what was going on in other timelines, on that exact date.
Extra points for the line to be placed at the exact same time of the day.
I am all down to spending whatever resources I have to help come up with a solution to this new feature. I am available 24/7 to help work/test/debug this.