C:\>perl -e "$x = 1.23456789012345e15; print $x;"
1.23456789012345e+15
C:\>perl -e "$x = 1.234567890123454e15; print $x;"
1.23456789012345e+15
C:\>perl -e "$x = 1.2345678901234544e15; print $x;"
1.23456789012345e+15