Quote from sim03:
The min/max chart shows the actual price extremes - the lowest bid and highest ask - during that minute. In a news-driven volatility explosion, the b/a spread is going to be only a small part of the range between those extremes, especially on a time frame as long as 1 minute.
To monitor the spreads in real time, click on the "Quote List" tab (rather than "Quote Panel") on your Current Rates window. To estimate the spreads after the fact, up to about 90 minutes, move the mouse across primarily sideways segments of the 5-second (rather than 1-minute) min/max chart. Finally, updated spread graphs are posted early next day - see the link by Wallace in the 2nd post above.
