A half-hour can be traded until gate closure, one hour before it starts; the line under the headline counts down to the next one, by your computer's clock. A worker follows Elexon's wind figures and prices, and recalculates the position when any of them changes. The farm is a share of Britain's wind fleet, so its output is the national figure scaled down. Half-hours still open for trading, which close an hour before they start, are valued at intraday prices that move every few seconds around Britain's market index price; the rest are valued at the market index price itself. Sold power comes from the portfolio's trades, which repeat every day. The portfolio also holds a made-up battery with a charge of its own. A worker plans its best use of the half-hours still open at the intraday prices, and the planned megawatts count in those half-hours' expected output. A positive open position is long: more wind than is sold, which settles at the imbalance price. "Today so far" adds up, for each half-hour since UK midnight that Elexon has settled (about 90 minutes behind), what the trades earned and what the farm's output not sold earned at that half-hour's system price; the battery is left out of it, as it has no measured output. All times are UK time. How your trades would come in says how a trader's own trades and market data would replace the made-up ones.