Helium is known to have emissions at 437, 468, 586, and 666 nm. The spectrum below might be obtained when the spectroscope is aimed at a gas emission tube containg helium.

When the known wavelengths are plotted versus the observed wavelengths, the equation of the line can be used to correct values obtained with a spectroscope for other gases.

Note: If plotting by hand, remember that the y-intercept of the line is where x = 0. If the axes do not start at the origin, the y - intercept cannot be read directly from the graph. In the example above, the y - intercept is -10.277, not about 400 nm.

Use the equation of the line to correct values obtained for other gases. For example, if the spectrum of xenon is viewed through the same spectroscope used to observe the spectrum of hydrogen shown above, wavelengths of 460, 450, and 440 nm may be seen. When these wavelengths are plugged into the equation y = 1.0024 x - 10.77 and the equation is solved for x, the corrected wavelengths of 470, 460, and 450 nm are calculated. These values agree much better with the known values of 467, 462, and 450 nm for xenon emissions.