My doubt is related to introducing a thin transparent film in one of the slits in YDSE. Yesterday, I understood that the net shift shouldn't be visible. I looked for some demonstrations online to understand this better. I got one in this video -
youtube.com/watch?v=dg5Ch0blQOI&t=338s - at t=5m38s, the central fringe shifting is visible and the pattern shift is visible unlike what we discussed yesterday.