Experimental data are seldom completely sampled. For example, a
spectrometer may have a bad channel, an image bad pixels and so on. To
handle this problem, GREG includes the notion of Blanking Value.
Most GREG data functions handle this blanking value which is defined
using command SET BLANKING Bval Eval
where Bval is the blanking value and Eval the tolerance for blanked data, necessary because of limited accuracy. Once a blanking value has been defined, all functions liable to handle it effectively use it. The default value can be overridden using the appropriate option /BLANKING. However some functions which should do it still do not handle blanked values ; this currently includes PERSPECTIVE.
To turn off the blanking value checking, you must specify a negative value for Eval, or simply use the command SET BLANKING/DEFAULT.
The blanking value can be used in two different ways :