I am in need of a formula to compare data in two columns and identify what data is present in one column but not the other.

e.g. Column A has data from last week, Column B has data from this week. I need to know if there were any new items this week, not present in the week before.

Can anybody help? Currently we are needing to manually go through the list (sometimes containing 1000+ items) and as you can imagine, this is very time consuming.

Any help would be greatly appreciated.