There are several renditions of the German #1 recticle.
The single post, like a front sight blade, as described by enfieldspares, is very fast to get on target. It is good for shooting men. Zeroed at 300 yards, you put it on the belt buckle when they are closer, up halfway at 400, top of the head at 500.
The thicker, tapered post, with a point like a obelisk, is good for dangerous game. Zero the point at 100. For 200 yards, use the base of the pointed part.
The ones like that with a thin horizontal line are helpful to stay lined up on game running across, like drive boar and stags.
The ones with an obelisk and thick horizontal lines are good in bad light on light-colored game, and in bright light they are good on dark game, as in putting the gap on a dark cape buffalo coming to get you.
A duplex with thicker lines and then fine in the center with a narrow gap is mighty good on a variety of game and in shooting conditions, fast enough on target, and capable for fine aiming.