Definition
In a numerical value, the digit that represents the smallest place value and therefore contributes the least to the overall magnitude of the number. In a decimal number, it is the rightmost digit; in a binary number used in digital avionics, it is the rightmost bit and represents the smallest increment the system can resolve.
Plain English
The digit on the far right of a number — the one that stands for the smallest amount and changes the total the least when it goes up or down by one.
Context Anchor
Seen in discussions of digital instruments, electronic displays, measurements, and computer-based aircraft systems.
Derivation
From 'significant' (Latin significare, 'to signify or mean') combined with 'least.' The phrase literally means the digit that signifies the least — i.e., contributes the smallest value to the number.
Why Pilots Care
Ensures accurate interpretation of precise instrument values, critical for navigation and altitude awareness.
Analogy
On a bathroom scale that reads 172.6 pounds, the 6 is the least significant digit. If it changes to 172.7, the reading changed by the smallest amount the scale can show.
Intuition Check
Do not read significant as meaning most important. Here, significant means the digit's place in the number, and the least significant digit is the smallest place-value digit.
Example Sentence 1
On the digital altimeter readout of 8,247 feet, the 7 is the least significant digit, showing altitude to the nearest foot.
Example Sentence 2
When entering the transponder code, pay attention to the least significant digit to avoid errors.