The S-band extends obliquely from the base of cell cu1 across r-m, reaching the anterior wing margin in cell r1, then following the anterior margin to the wing apex. This ratio is the width of the S-band at the apex of vein R2+3 divided by the width of cell r2+3, both measured perpendicular to the long axis of the band and the costal margin at the apex of R2+3. The width of the distal section of the band and the width of cell r2+3 are measured along the same line, both measurements including the width of the costa (i.e., the measurements begin on the external margin of the costa). The ratio cannot exceed 1.0.