This tool is meant to help you learn the different types of gaps:
GNG = Gap N Go (flag icon). This occurs
RTG = Retest Gap (x icon)
SETTINGS
Gap Size: Will display a green(bullish) or red(bearish) icon. The 2% (default) gap size will highlight gaps that are greater than the configured setting (2% up or 2% down).
NOTES
The gap size is measured from the previous day CLOSE to the current day OPEN and ignores the current days movement.