Yeah, to get the maximum value I must deactivate any measures.
8bit/10bit plays a role too and switching from fast to slow acquisition, this thing do it´s business...
Nevertheless, in my opinion it´s too wide apart from the specs.
Done this as I said before with the rigol, it matches exactly the specs and more.
Also the trigger-signal from the rigol was so stable, that counter and scope measurings was equal.
So what´s going on with the siglent...
To be honest, that doesn´t worrying me in a matter, I would give it away.
But I find it remarkable enough to expect an official explanation for it.
Edit: Forwarded this to the siglent support.