Changing the value of a custom field when changing the price

Hi,
I have two custom fields: cost and result.

To simplify, Result must have the value ( full price – cost) / 100

When the value of full price or cost is changed from bulk I need the custom field result to be updated according to the formula written before.

I have tried using woobe_before_update_product_field. In the DB the value is updated. The problem is that to see it in the bulk I have to refresh the page otherwise I always see the old value.

How can I solve this? Is the hook I am using the correct one?
Thank you.