Keysight Technologies 3458A Guide D'utilisation page 143

Making Measurements 4
S = sign bit (1 = negative 0 = positive)
E = base two exponent biased by 1023 (to decode these 11 bits, subtract 1023
from their decimal equivalent).
M = mantissa bits (those right of the radix point). There is an implied most
significant bit (MSB) to the left of the radix point. This bit is always "1". This
provides an effective precision of 53 bits with the least significant bit (right most)
-52
weighted 2 . Another way to evaluate this mantissa is to convert these 53 bits
-52
(MSB = "1") to an integer and then multiply by 2 .
The value of a number in the DREAL format is calculated by:
S (exponent)
× ×
(-1) (mantissa) 2
Keysight 3458A User's Guide 143