When you are working on a recipe and it lists the IBU for a hop entry, do you alter the recipe to make sure you hit that IBU or do you just follow the guideline for amount? So far I've just ignored the IBU and followed the recommendations for weight but on the pale ale I'm about to brew I had to substitute for a different hop. So I'm wondering if I should just tweak the amount until I hit the IBU suggested in the recipe.