In the years, that I have been making bread, I discovered an important issue that causes a great deal of inconsistency in the bread making process.
If you measure your flour by volume, you run the risk of having an error ranging from 0% to +25% in your quantities.
For this reason, I measure Flour and liquids by weight.
What follows is a visual demonstration of how the error occurs.
Step 1: Same Weight - Different Volumes
In each of the two jars above, I have place one pound or 450 grams of flour.
I then took the jar on the right and gently tapped it on the table to make the flour settle and drive out any air.
I also took the jar on the left and shook it the way you would shake a cocktail to aerate it. This is the same effect as running flour through a sifter. It is getting air mixed between the minute flour grains, thus making it occupy more space.
The ruler is two show you the difference in volume occupied by the same weight of settled and aerated flour.
On the right, the flour reaches 3 1/4"
Ob the left, the flour reaches 4 1/4"
Same weight by different volumes
Step 2: Compare When You Used Water for the Same Volume.
Now replace the flour with water in the same jars.
The flour respectively reached 3 1/4" and 4 1/4" for the settled and aerated flours.
The difference turned out to be exactly 1 cup of water.
It just happens that with these jars (Jiff Peanut Butter) each inch represents 1 cup with the 1/4" at the bottom is from the taper of the jar.
1 1/4" = 1 cup
2 1/4" = 2 cups
3 1/4" = 3 cups
4 1/4" = 4 cups
Step 3: The Error.
The difference between 3 and 4 cups of flour, is in effect an error of 25%
A 25% error in one ingredient can make or kill your recipe.
And if you don't adjust for it, by either weighing your flour every time, or making sure that your flour is settled every time you measure by volume, you results will vary every time.
In the case of bread, you will struggle with crumb that varies from light and bubbly, to dense and compact.