$x->digit($n);          # return the nth digit, counting from right
$x->digit(-$n);         # return the nth digit, counting from left 

##</code><code>##

13:45 >perl -MMath::BigFloat -wE "my $n = Math::BigFloat->new(123); say $n; say $n->digit(-1);"
123
Can't use an undefined value as an ARRAY reference at C:/Perl/Strawberry/strawberry-perl-5.18.2.1-64bit-portable/perl/lib/Math/BigInt/Calc.pm line 1209.

13:45 >p5u v Math::BigFloat
Math::BigFloat
        C:\Perl\Strawberry\strawberry-perl-5.18.2.1-64bit-portable\perl\lib\Math\BigFloat.pm: 1.998

13:46 >