What exactly is significand?

Question

per wiki, The significand is part of a number in scientific notation or a floating-point number, consisting of its significant digits.

in this example $$123.45 = 0.12345 × 10^3$$

which part is The significand? is it 0.12345? or just 12345

Answer 1

In general, the significand is the part that varies depending on the measurement precision. In standard form (a number written like $a \times 10^{n}$), the significand is $a$, which is the original number stripped of all leading and trailing zeros. Clearly, the number of digits of $a$ tells us how precise the number is, and $n$ just tells us the order of magnitude of the number.

There is no real consensus on whether the significand should be an integer, or be between $0$ and $1$, or anything else. In your case it could be either depending on how you choose to express it. If you are writing the number as $0.12345 \times 10^3$, then the significand certainly is $0.12345$.