Hβ vs. continuum flux. Upper plot: all observed data. Bottom: without the data from the Zeiss telescope. The continuum flux is plotted in units of 10^-16 erg cm^-2 s^-1 Å^-1, the line flux in units of 10^-14 erg cm^-2 s^-1. Observations with different telescopes are denoted with different symbols given in the upper left corner. The correlation coefficient and the corresponding p-value are also given.