 The measured shifts in wavelength are fractions of a picometre.Measuring the full spectral profile of the line with this precision requires a high-dispersion spectrograph and a long time to collect sufficient photons to make the measurement with precision.For example, SOLIS requires about an hour to gather polarized spectral profiles over the whole Sun, and Hinode, the recently launched spacecraft with a 0.5-meter solar telescope on board, takes about an hour to cover a 164-arcsecond-square field (1% of the Sun) at very high spatial resolution.