Barbieri Spectro LFP qb Operating Manual page 38

When the "TEX" option (Textile activation) is activated on the instrument
and using the Barbieri Gateway software or any software supporting
this option, the sensing unit will capture a picture of the inserted chart,
measure and analize it and deliver information about chart size, chart
type, chart position etc.
There are 4 black marker points on the surface of the

instrument indicated in red in above image.
These markers are used by the sensing unit as fix
points to correctly calculate metrics.
For a correct functionality of the metric algorithms
it is important to make sure these points are visible
to the camera and not covered by the chart inserted.
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Spectro LFP qb - Operating Manual