watchpoint for Internal table value

Hi  Friends,

how to put a watch point for a Internal table, field value.

Ex : I have a Internal table called "IT1" in this table we have 10 fields &  9000 records.

for 600th record some value "ABCD" is updating in the code ex : IT1[600]-FIELD1 = "ABCD",

but I want to know where this value is updaing.

for this I want to put a watch point.

I have read many forums but doesn't meet the requirement.

Can any one please help me on this.