Seems to me that one of your array indices is pointing to la-la land. My guess is that your bounds checks in your working code (the "if c >= CALIB_..." and "if p >= CALIB_...") prevent the lookups using c and p from blowing up.

You might also want to consider simplifying your data structure. The nested arrays and arrays-of-structures can get pretty ugly.

Hopefully you've statically-declared all of the arrays rather than using pointers and malloc().

-a