> If you set it up to sell when the prices drops to $320, you are guaranteed that it will sell at a price below $320, not that it will sell at $320.
IIRC, that’s closer than the naive interpretation (“you will sell at exactly $320 if the price drops to or below that level”), but it's still not quite right. Unless I'm mistaken, a stop-loss @ $320 is actually “if the price is at or below $320, submit a market sell order”. In theory, it could execute above $320, though at or below is vastly more likely. And, as you note, you aren't guaranteed it will execute at all.
IIRC, that’s closer than the naive interpretation (“you will sell at exactly $320 if the price drops to or below that level”), but it's still not quite right. Unless I'm mistaken, a stop-loss @ $320 is actually “if the price is at or below $320, submit a market sell order”. In theory, it could execute above $320, though at or below is vastly more likely. And, as you note, you aren't guaranteed it will execute at all.