precision, or maximum width
You can specify a precision (for numeric conversions) or a
maximum width (for string conversions) by specifying a "."
followed by a number.  For floating point formats, with the
exception of 'g' and 'G', this specifies the number of
decimal places to show (the default being 6), e.g.:

# these examples are subject to system-specific variation
    printf '<%f>', 1;    # prints "<1.000000>"
    printf '<%.1f>', 1;  # prints "<1.0>"
    printf '<%.0f>', 1;  # prints "<1>"
    printf '<%e>', 10;   # prints "<1.000000e+01>"
    printf '<%.1e>', 10; # prints "<1.0e+01>"

For 'g' and 'G', this specifies the maximum number of
digits to show, including prior to the decimal point as
well as after it...