The Chevron and Fougere patterns are very similar as both have chevrons between two lines. As you can see in the pictures of the solid 18K Presidentials, they do have some differences. (Chevron is on top in each photo of the pair.)
Here is a closer view of the pattern differences.
As you can see the Chevron pattern has multiple rows of chevrons between the longitudinal lines going done the length of the cap and barrel, whereas the Fougère pattern only has one distinct row.