This parameter sets the lower extraction limit for the dekker in the spatial direction.
A non-zero value for this parameter will over-ride the automatic dekker extent calculated by ECH_SPATIAL.
TUNE_DEKBLW can be used when the dekker extent and position relative to the order traces are well knwon. Typically, it will be used when the first of a set of similar frames has been manually extracted and automatation of the extraction of the remaining frames is required.
INITIAL SUGGESTED VALUE: 0.
Martin Clayton