I'm working on a stock sheet which lists products, their batch numbers, number of products left, and various other information.

Sometimes there are several different entries of the same product number but with different batch numbers. (The number of entries for the same product can go up and down as stock is used up and more is bought in.)

For each product, there is a specific quantity when, if stock goes below that number, more stock should be ordered.

I want excel to highlight whenever a product goes below its specific quantity.

What is the best way to do this, when there are often several entries for the same product, and the number of entries can vary?

I'd really appreciate your help!
(Do say if I need to explain this in more detail.)