According to my literature, there was no Binova in 1988, and the colour (Icy Pink fade to white) does not match 1987, so it should be 1985 or 1986. Check the bottom of the seat tube, in the vicinity of the front derailleur mount, for the serial number.

Most butted seat tubes are single butted. The thick end goes is at the bottom to stiffen the bottom bracket area under hard pedal strokes. The top end is thinner and the same thickness as the middle, because the seat post itself adds strength to this portion of the tube.

Plain gauge seat tubes are the same thickness along their entire length to cut manufacturing costs. Without the thinning in the middle and top , they are heavier and require a smaller diameter post.