Thank you Monks! I'm still struggling to isolate the problem to an SSCE but did make an interesting discovery. Turns out the math is not causing the error. I though it was because commenting that line out eliminated it. Just before doing the math I use "int" on one of the numbers. If I don't use "int" the program works! It also works if "int" is used and "use bignum" is commented out AND this is done: Math::BigFloat->config({ div_scale => 1 }); (don't need to use Math::BigFloat, cause I guess Astro::Units already loaded it). I have no idea what is going on but will just not use "int". Hope this makes sense. Thanks again!