Unfortunately, there is a major error in describing the "set trigger" and the "hair trigger" of the Berdan Sharps in this video. I've owned two Berdan Sharps and sold one of them to Don Troiani who found it had been issued to the Penn. Bucktails by the serial number in the archives. The Berdan Sharpshooters were armed with these new rifles with double set triggers in May and June of 1862 when their combined strength had dwindled to about 1,000 men. Because 2,000 of these rifles were available, the excess were placed in the Washington, D. C. Arsenal. Inevitably, some of these Berdan Sharps rifles that had been in storage for the wounded were taken by the Penn. Bucktails. (see Wiley Sword's SHARPSHOOTER: Hiram Berdan, his famous Sharpshooters and their Sharps Rifles) for more information on this subject.
First the rear trigger is "set" but squeezing it. That makes the front trigger a "hair trigger" and this is the one you squeeze with your trigger finger to fire the rifle. NOT the other way around as described by the NPS person in the video. There is a small screw between the two triggers that can be tightened to put pressure upwards on the sear so that there is less and less surface area of the front trigger against it. In this way, you can set it to a very light pressure to fire the rifle or a little stiffer pressure -- whichever you preferred. It doesn't take any time to learn this either. These Sharps rifles with double set triggers were issued to the rank and file -- not merely officers in the Sharpshooters (another mistake in the video).
The benefit is that when you have your sight picture on the target, you won't be pulling the rifle off target with a heavy trigger pull as found on many rifles. I've owned over a dozen Sharps rifles with double set triggers as these were used in the 1874 model sporting rifles and I've built 4 muzzle-loading Hawken rifles with double set triggers as it makes for a much more accurate rifle with such a light trigger pull on the FRONT trigger.
I had a distant cousin, First Sgt. Lewis J. Allen, in Co. F (the Vermont Company) of the 1st USSS who was at Pitzer's Run and later wounded at the Wilderness where I had another Allen ancestor KIA and still another who died of wounds a week later.