EXFO FTB-500 (Window XP) - Manual (Page 374)

Data Types
366 FTB-500
Applicable Data Types for Output —IEEE 488.2

(or )
This data type will be used by a device to return positive or negative
integers.
Examples: 4, –23, 90

(or )
This data type will be used by a device to return positive or negative
real numbers (fixed-point numbers).
Examples: 23.45, 1.22, –4.55
+
-
.
+
-