Thanks for your answer! Sure I will give it a try...
It's just a simple problem, but hard to explain...
First of all, I tried several functions. It doesn't matter if I use Triangular or Sine or any other.
#1 I try to measure a simple signal (i.e. Rect, Sine or Triangular Wave). Doesn't matter what kind of wave it is!
#2 Upper part of the picture
You can see in the upper part of the picture a Triangular Wave. It is triggered with the "Rising" Slope. Ok? So I got the upper wave and that's ok for me. But...
#3 Lower part of the picture
In the lower part of the picture you can see the same Triangular Wave with the same configuration of the scope. It is triggered with the "Rising" Slope, too.
The displayed wave is now different from the upper once, but it should be the same! Do you understand?
The displayed wave changes at random between the upper and lower wave during my measurement. So I can say that Trigger Option "Rising" or "Falling" is out of order.
If I use another analog or digital scope the upper wave (upper pic) is triggered with "Rising" slope and the lower wave (lower pic) is triggered with "Falling" slope. But PS3205 changes at random, doesn't matter if I choose "Rising" or "Falling".