As noted in the mechanical drawing, there are two possible widths for the Studiolive 24.4.2: 23.61" and 25.19". This is because the plastic "wings" on the side of the StudioLive 24.4.2 can be unscrewed and removed, reducing the mixer's width from 25.19" to 23.61".
In addition, the mixer can be equipped with "ears" for rackmounting. With the rack ears installed, the total width of the Studiolive 24.4.2 is 25.39".
For more information about how to remove the plastic wings and install the rack ears, check out this link.