deletions | additions       diff --git a/sectionINTRODUCTION_.tex b/sectionINTRODUCTION_.tex  index 651c171..f4cc6d1 100644  --- a/sectionINTRODUCTION_.tex  +++ b/sectionINTRODUCTION_.tex 
...
\section{INTRODUCTION}   Reliability is defined as the ability of a system to serve a given function over time.  Reliability of particle accelerators is very important for user facilities, like storage ring based light sources;  but it is as well an important design objective for new types of facilities as accelerator driven systems or   new large scale facilities as for example the International Linear Collider.  An operation metrics should quantify the reliability of a particle accelerator.  The calculation of operation metricsfor an accelerator serves several purposes:   it  can be used to  quantify the improvement of a specific facility over time, orit can be used  to compare the performance of similar facilities. In the first case one should select operation metrics' in line with the user requirements~\cite{Luedeke:2014aa}. requirements of that specific facility~\cite{Luedeke:2014aa}.  For the latter case the metrics for compared facilities should follow a common standard.  In particular beam availability is often used to compare the reliability of  light sources. While these statistics are published for most light sources, few facilities do supply definitions on how these numbers are calculated. A survey of several light sources revealed~\cite{L_deke_2009} that the calculation of this metric varies considerably.   The conditions under which beam is considered available are often defined in common sense terms,  and even if there are formal definitions, they differ between facilities.   But Furthermore a large variety of failure modes is often convoluted into ``beam not available'',   commonly called ``downtime''.  Since some of these failure modes are specific to individual facilities,   this further complicates the comparison of beam availabilities.  %But  if beam availability is not identically defined, then the metric is less useful for a meaningful comparison. Our aim is to propose simple, well-defined, formal operation metrics for storage ring light sources,   to make the reliability of these facilities comparable.   The metrics serve to clarify for each facility the beam parameter promised to the users,   and the statistical data reveal, how well the standards are met. The authors are convinced that this metrics will refine our ability  to learn from the reliability comparison of light sources.