EXFO FTB-2 - Manual (Page 372)

IEEE 488.2 and Specific Command Reference
362 FTB-2 and FTB-2 Pro
Specific Commands
In ASCii format, the numeric data is transferred
to ASCii bytes in <NR1 NUMERIC RESPONSE
DATA>, <NR2 NUMERIC RESPONSE DATA> or
<NR3 NUMERIC RESPONSE DATA>
representation, as appropriate.
In PACKed format, data is transferred to a
<DEFINITE BLOCK RESPONSE DATA>, in a
manner specified in the device documentation.

Length:
The program data syntax for <Length> is
defined as a <DECIMAL NUMERIC PROGRAM
DATA> element.
When ASCii data format is selected, the optional
<Length> parameter specifies the number of
significant digits to be returned. A <Length>
value of zero indicates that the device selects the
number of significant digits to be returned. When
a <Length> of zero has been specified, the
FORMat[:DATA]? query returns zero as its second
parameter.
When the PACKed data format is selected, the
optional parameter <Length> it not used.
Example(s) FORM ASC
FORM ASC,6
FORM:DATA PACKED
See Also FORMat[:DATA]?
:FORMat[:DATA]