Timestamps For Read operations:
If TS (T) < W-timestamp (Q), then the transaction T is trying to read a value of data item Q which has already been overwritten by some other transaction. As the value which T wanted to read from Q does not be there anymore, and T would be rolled back.
If TS (T) >= W-timestamp (Q), then the transaction T is trying to read a value of data item Q which has been written and committed by some other transaction earlier. As T will be allowed to read the value of Q, and the R-timestamp of Q should be updated to TS (T).