I'm feeling very confused about which sign to the potential should I choose. A specific exercise I've had trouble with is in this link. in this exercise a double Atwood machine is given. when I tried calculating the potential, I drew gravity pointing downwards, and the axis system I chose was y pointing downwards and x pointing right. I chose the reference plane to be the canter of the top pulley (marked in green in the picture). so when I calculated the total potential energy V, for all the masses, I got the same expression as in the article, but in an opposite sign. What did I miss?
Thank you very much for your help.