As we move toward later (cooler) types, the helium lines continue to fade until they essentially disappear in spectra of this resolution (1.8 Å) at a spectral type of about A0. Again, the ratio He I 4471/Mg II 4481 is useful in determining the spectral type in the late B-type stars. At A0, the Ca II K-line becomes a notable feature in the spectrum (in the B-type stars, the K-line often is mostly interstellar), and increases dramatically in strength as we move toward later spectral types. However, it is well to keep in mind that in the peculiar A-type stars and the metallic-line A-type stars (see below), the strength of the Ca II K-line is almost always too weak for the spectral type. In addition, the general metallic-line spectrum, almost invisible in the B-type stars, becomes evident and strengthens through the A-type stars. Useful lines and blends in the determination of the spectral type in the A-type stars (such as Mn I 4030, Ca I 4227, and Fe I 4271) are labeled underneath the spectra. The Mg II 4481 line changes little in strength in the A-type stars.