How to stop or freeze a cell value from further updating after condition is met in EXCEL


Hello traders,

i’m creating a custom screener in excel. from an external source i’m linking the LTPs of stocks in excel.
since the LTPs are constantly changing as the stocks move bUT i want to fix or freeze a particular cell after a condition is met say for instance, if LTP is > HIGH should give me BUY SIGNAL which i have done using IF condition but since LTP is dynamic and keeps on changing ,it will highlight the cell but again if LTP ticks down , the cell value will not highlight. i want this to stop once the condition is met.

in other words i want the excel to tell me hi, LTP has crossed the HIGH and should stay highlighted no matter what the LTP is now

any tricks for this??? please let me know