problem with using arduino to get analog input. setting in "analog input" block , "gain block"

I use the "analog input" block to get the voltage of an potentiometer, and I want to display the value. I use a gain block after the analog input block,and set the gain to 5/1024 since the "analog input" block gives digital value from 1-1023,and the output data type is already set to double, but the display always shows zero. my arduino works well, I can get the value by using read voltage command in command window. I want to do something like this https://www.youtube.com/watch?v=xFSgbRqK_9A but it seems i use "analog input" block in a wrong way. is there anything wrong with the settings in "analog input" block , "gain block" please help! thanks!