hi i am trying to make a 220 ac to 12 dc converter but something is wrong with the alternator i put 220v and 50 hz in parameteres but in the the ossliscope it shows a max of 155 v
for a voltage measurement you need two wires.
The volt_meter / scope uses GND and the signal_input (in your case Ch A). It displays the voltage "CH_A - GND"
But your input is not GND referenced. So both signal source connetions are floating somehow.
--> I assume connecting the lower side of your signal source to GND gives the expected values.