function fraction = bsfrac
% bsfrac Returns fractional width of binary search bracket [PHYS210-bs]
   global Bs_low Bs_high Bs_tol Bs_progress;
   if ~ bsinitialized
      warning('Search not initialized.  Use bsnew(low, high)');
      return;
   end
   if bscurrent == 0
      fraction = Bs_high(end) - Bs_low(end);
   else
      fraction = (Bs_high(end) - Bs_low(end)) / bscurrent;
   end
end
