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7.5 Reading index
The tape reading at the height of the reading index of the
instrument is indicating the distance between the reaction point
and the reading index. If the instrument is installed in such a way
that the reading index is at the same level as the zero-ullage
reference level the reading of the tape corresponds to the ullage
providing the reaction point of the sensing probe is positioned
at the liquid level.
If the reading index is positioned below or above the reference
level a positive or negative correction of the tape reading is
necessary.
See also chapter 8 “Examples of installation of the gauging
system”.