anchor.diff:         & SENSE_POSITIVE = 1, &
          & SENSE_NEGATIVE = -1
   
  -  ! Used for surface current tallies
  -  real(8), parameter :: TINY_BIT = 1e-8
  -
  -  ! Maximum number of collisions/crossings
  -  integer, parameter :: MAX_EVENTS = 10000
  -  integer, parameter :: MAX_SAMPLE = 100000
  -
  -  ! Codes for read errors -- better hope these numbers are never used in an
  -  ! input file!
  -  integer, parameter :: ERROR_INT  = -huge(0)
  -  real(8), parameter :: ERROR_REAL = -huge(0.0_8) * 0.917826354_8
  -
  -  ! Source types
  -  integer, parameter ::   &
  -       SRC_BOX     = 1, & ! Source in a rectangular prism
  -       SRC_CELL    = 2, & ! Source in a cell
  -       SRC_SURFACE = 3    ! Source on a surface
  -
  -  integer, parameter ::        &
  -       PROB_SOURCE      = 1, & ! External source problem
  -       PROB_CRITICALITY = 2    ! Criticality problem
  +  ! ============================================================================
  +  ! CROSS SECTION RELATED CONSTANTS
   
     ! Interpolation flag
     integer, parameter ::     &
  
positive.code:        ACE_THERMAL   = 2, & ! thermal S(a,b) scattering data
         ACE_DOSIMETRY = 3    ! dosimetry cross sections
  
    ! Tally macro reactions
    integer, parameter :: N_MACRO_TYPES = 15
    integer, parameter :: &
  
negative.code:        ONE          = 1.0_8,             &
         TWO          = 2.0_8
  
    ! ============================================================================
    ! GEOMETRY-RELATED CONSTANTS
  
    ! Boundary conditions
    integer, parameter ::    &
  