Signed-digit representation of numbers indicates that digits can be prefixed with a − (minus) sign to indicate that they are negative.
Signed-digit representation can be used in low-level software and hardware to accomplish fast high speed addition of integers because it can eliminate carries. In the binary numeral system one special case of signed-digit representation is the non-adjacent form which can offer speed benefits with minimal space overhead.
The non-adjacent form does guarantee a unique representation for every integer value, as do balanced forms.
When representations are extended to fractional numbers, uniqueness is lost for non-adjacent and balanced forms; for example,
Such examples can be shown to exist by considering the largest and smallest possible representations with integral parts 0 and 1 respectively, and then noting that they are equal. (Indeed, this works with any integral-base system.)