Let us consider a cell B2 where data validation in puts are a, b, c. Now if you put ‘k’ in the cell B2 then a message box will come “The value entered is not valid”, but if you off the ‘error alert’ option in data validation box, then the cell take the value ‘k’ without any notice. In that case for searching invalid data in the entire sheet- first you select whole sheet and then click ‘circle invalid data’ the cells containing in valid data (in this case the cell B2) appearing with a red circle. For removed the circles, again select the selected cells and click ‘clear invalidation circles’ the red circles will disappear.
