  We present a new solar flux atlas with the aim to understand wavelength
precision and accuracy in solar benchmark data. The atlas covers the wavelength
range 405--2300 nm and was observed at the Institut f\"ur Astrophysik,
G\"ottingen (IAG) with a Fourier Transform Spectrograph. In contrast to other
FTS atlases, the entire visible wavelength range was observed simultaneously
using only one spectrograph setting. We compare the wavelength solution of the
new atlas to the Kitt Peak solar flux atlases and to the HARPS frequency-comb
calibrated solar atlas. Comparison reveals systematics in the two Kitt Peak FTS
atlases resulting from their wavelength scale construction, and shows
consistency between the IAG and the HARPS atlas. We conclude that the IAG atlas
is precise and accurate on the order of $\pm 10$ m s$^{-1}$ in the wavelength
range 405--1065 nm while the Kitt Peak atlases show deviations as large as
several ten to 100 m s$^{-1}$. We determine absolute convective blueshift
across the spectrum from the IAG atlas and report slight differences relative
to results from the Kitt Peak atlas that we attribute to the differences
between wavelength scales. We conclude that benchmark solar data with accurate
wavelength solution are crucial to better understand the effect of convection
on stellar RV measurements, which is one of the main limitations of Doppler
spectroscopy at m s$^{-1}$ precision.
