When the sample is removed, the refractometer goes to NO SAMPLE state. However, if skip count is greater than 0, the CONC is frozen to its last value for the number of measurement cycles (one per second) indicated by skip count. Typically skip count is used when there are large voids in the process liquid. For example a setting of 10 measurement cycles ensures that any NO SAMPLE state shorter than 10 seconds will not make a dip in the output signal.
Skip count is set in the Output settings section of the parameter page.