Risk & Lot Sizing

With Use Risk % off, every entry uses Lot Size. With it on, the terminal sizes each entry so that a loss at Stop Loss costs Risk % of the account balance, using the broker's contract details for the symbol. The size is rounded down to the broker's lot step, never up. Risk % works on MT5 and BloFin; on MT4 and Rithmic the terminal refuses START with Use Risk % ticked. If it cannot size a trade (unknown contract details, a profit currency other than the account's, a size below the broker's minimum or above its maximum), START is refused, or while running the entry is held, and the Trade Log says why; with Stop Loss at 0 it trades the fixed Lot Size and says so.