These flame-sealed cells contain 400 Torr of >99.9% pure methane (CH₄) at room temperature. They are used for calibration of tunable lasers in the 430-1050 nm range. While most of the absorption lines are very weak, except in the ranges of 3050-3650 nm, the alkane C-H stretch region, and 7275-8300 nm, the C-H bend region, the lines are highly accurate due to the high symmetry and simplicity of methane.

The quartz cell body is cylindrical in shape; outer diameter 10 mm; length 75 mm. The tipoff stem is centered on the cell, protruding not more than 8 mm from the cell body. Windows are angled 11° off of normal and have a 2° interior wedge to prevent back-reflection and etalon effects.