The SGBV is a fixing market. Orders aren't matched continuously through the day like on the NYSE or Euronext. Instead, the exchange collects buy and sell orders during a pre-fix window, then strikes a single clearing price that maximises the volume that can trade. Every order that executes that session executes at that single price.
That means: there is no intraday tape, no live candle, no 1-minute chart. A ticker's daily "close" IS its open, IS its high, IS its low. The chart on this app is one bar per session for that reason.
Most SGBV equities fix three days a week (Sunday, Tuesday, Thursday). OAT and SME compartments have their own calendars. The Pre-fix tab in /market shows the buy/sell imbalance ahead of the next auction.