uncertainty of measurement and Sig figs

Significant figures

All certain numbers (digits) and one uncertain number (estimate)

Exact number

Number whose value has no uncertainly

Inexact number

Number whose value has some uncertainty associated

Leading zeros

Zeros at the beginning of a number ( are not significant figures )

Confined zeros

Zeros between non zero digits (are significant)

Trailing zeros

Zeros at the right end of the number (only significant if number contains decimal point)