Concept:
A micrometer is a precision measuring instrument used to measure small dimensions accurately.
Step 1: Least count is the smallest value that an instrument can measure.
Step 2: A standard micrometer screw gauge can measure very small lengths.
Step 3: Its least count is commonly:
\[
0.01\,mm
\]
Step 4: Therefore, the least count of micrometer is \(0.01\,mm\).
\[
\boxed{0.01\,mm}
\]