# FLOYDS pipeline step by step

\label{sec:step} In this section we will describe in detail each step of the pipeline, focusing on the output.

## Wavelength calibration

\label{sec:wcalib} The lamp used for calibration is an HgAr lamp. In most arcs 20-30 lines are clearly visible and widely distributed along the first order, while 5-10 lines are visible in the second order. Since the geometrical rectification is already providing a rough wavelength calibration, a low legendre polynomial order is used to better solve the wavelength calibration. An arc file from the archive is used as reference, which for most cases gives the wavelengh calibration without need of adjustment from the reducer. An example of the line identifications is shown in Figs. \ref{fig:blueident} and \ref{fig:redident}.

The following keywords are usually added to the science frame to keep track of the accuracy of the calibration:

SPERES_R=     474.2613249124601 / Spectral resolving power
LAMRMS_R=               0.0189 / residual RMS [nm]
LAMNLINR=                 16.0 / Nb of arc lines used in the fit of the wavelengths
SPE_ER_R=             0.004725 / statistical uncertainty
ARCRED  = arc_nttPSN031752_fts_20130730_red_2.0_56504_1_ex' /  reference arc
DCLOG2  = REFSPEC1 = arc_nttPSN031752_fts_20130730_red_2.0_56504_1_ex'
SHIFTR  =                 -5.0