[0] Perl> printf "%12.6g\n", $_ for map{ "1.23456e$_" } -12 .. +12;;
1.23456e-012
1.23456e-011
1.23456e-010
1.23456e-009
1.23456e-008
1.23456e-007
1.23456e-006
1.23456e-005
 0.000123456
  0.00123456
   0.0123456
    0.123456
     1.23456
     12.3456
     123.456
     1234.56
     12345.6
      123456
1.23456e+006
1.23456e+007
1.23456e+008
1.23456e+009
1.23456e+010
1.23456e+011
1.23456e+012