<h3>Data Gap</h3>
  Every parameter from the expression is preprocessed before expression evaluation. 
  It is resampled (averaged or interpolated) with taking into account possible absence of data (data gaps).
  Here you may define 'gap threshold'.
  It is expressed in the parameter 'sampling times.
  If data is absent for time interval greater than this threshold the interval is treated as 'gap', 
  otherwise the interval is filled with the interpolated data. 
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