 It can be studied using nearby stars, for which independent distance measurements are possible, and it can be expressed in a simple analytical form.In other words, the Wilson–Bappu effect can be calibrated with stars within 100 parsecs from the Sun.The width of the emission core of the K line ( ) can be measured in distant stars, so, knowing W0 and the analytical form expressing the Wilson–Bappu effect, we can determine the absolute magnitude of a star.