I calibrated both channel but the reading on Vdd and Vpp are very far from the right value.
I tried to re-calibrate but without chance.
It works in this manner or there something I can do??? 
the measurement are caculated by the wave form on the screen in the firmware, it has something to do with the probe calibration and the voltage calibration. so i suggest you do the calibrations carefully. and also, i admit that the measurement is not very precise because of the measurement algorithm in the firmware.
So I re-calibrated the probes and re-calibrated both channels.
I used a stable and well filtered source, a very good multimeter and a “real” digital oscilloscope.
I tried to source the requested voltage (5 to 6 times the division) and once (for an entire calibration) I sourced 10 times the division voltage. I left out only the last because I had only 25V (so i entered that value).
I got the “…saving calibration data…” message (note: here spelled how i remember 
But I never get an accurate voltage measurement.
The 0V is ever distant from 0!
Can be faulty my unity?
I did a lot of calibrations, like 10 times, and any time the calibration is good.
After calibration, when I put the probe on GND, it shows 1.4 VDC in 10V scale, innaceptable.
I would like to know if there is some chance I get correct calibration values. I will try to use older firmware, because it seems to get better calibration results.