$ perl -lwe 'use Devel::Peek; my $x = 15; $x += .1 for 1..10; Dump $x; print $x; printf "%.20f\n", $x'
SV = PVNV(0x8151ff0) at 0x814f69c
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,NOK,pNOK)
  IV = 15
  NV = 16
  PV = 0
16
15.99999999999999644729