Definition
In a binary number, the least significant bit (LSB) is the bit that represents the smallest value — the rightmost bit in standard binary notation. Changing it alters the number by the smallest possible amount (a value of 1), while changing the most significant bit alters the number by the largest amount.
Plain English
In a string of binary digits (1s and 0s), it is the digit on the far right — the one that counts for the smallest amount. Flipping it changes the number by just one.
Context Anchor
Seen in avionics, digital instrument, transponder, encoder, and maintenance manual discussions where information is stored or sent as binary numbers.
Derivation
From the binary numbering system, where each bit position represents a power of two. The rightmost bit represents 2⁰ (which equals 1), making it the smallest — or 'least significant' — contributor to the total value.
Why Pilots Care
Pilots rarely deal with bits directly, but in modern glass cockpits and digital systems, the precision of displayed values (altitude, position, fuel quantity) depends on how many bits a system uses and how the least significant bit is defined. A coarser LSB means less precise data.
Analogy
Think of a four-digit odometer. The rightmost digit changes every mile — it's the 'least significant' because it represents the smallest unit. The leftmost digit only changes every thousand miles. Binary works the same way, just with 1s and 0s instead of 0–9.
Intuition Check
Do not read least significant as meaning unimportant. Here it means the bit with the smallest numerical value in the digital number.
Example Sentence 1
The digital altimeter encodes altitude in binary, with the least significant bit representing one-foot resolution.
Example Sentence 2
Technicians verify data bus integrity by confirming the least significant bit toggles correctly during a test sequence.