Sarah talks about using horizontal balance lines on garments for a better fit. Sarah has written about this in her article about How to make a mock-up.
Making a mock up pants pattern with both the grainlines and horizontal balance lines will help you identify where the pattern needs adjusting for a better fit.
The horizontal balance lines (hbl) will show if the centre back seam needs more or less length.
Sarah recommends drawing 3 hbls on the pants mock up. The first across the widest part of your buttock and then two more hbls. One hbl 5 cm above the first hbl and one 5cm below the first hbl.
The grainlines will show where you need more or less fullness. When the grainlines start to angle across the body, that tells you the crotch needs to be scooped! Pinning the crotch curve allows you to see how much scoop is needed to straighten the grainlines.
Changes to the centre back seam can affect the front of the pants.
Sarah talks indepth about crotch lengths required for a good fit and ensure you have the correct proportions.
When Sarah talks about walking a pattern, this is the process of matching up stitching lines of each seam, to determine if the seams will line up correctly when sewn in fabric. You’re checking the seam lines are the same length
In some cases the stitching lines will be exactly the same length, which is straightforward matching: centre front and centre back seams are almost always the same length.