Validation Query

Hi All!

I already have 4 records in the grid. While creating a new record in the grid, the sum of Mark1 has to be calculated & if it is >=200, it should display an info message. While inserting the fifth record, the fifth record's Mark1 is not getting considered. Only the existing records' Mark1 is considered. So, the validation is not working. How can I do this?

Thanks in advance!