Need formula,command or IF statement

StephenDC  this also sounds like a perfect application for Conditional Formatting.  Conditional Formatting won't insert a value like 'Hi' or 'Lo' but can/will highlight cells.  If you need to export the sheet or use those 'flags' in other references then conditional formatting won't work, but if it is just for you to quickly see or find those values, conditional formatting is the way to go.