in reply to maths-thing
One suggestion I can think of right off the top of my head is to say: chomp($time = <FILE>), instead of $time = <FILE>; chomp $time;, but that's really just a matter of taste.
Also, you might want to consider indenting the contents of subroutines, the subby at the end is a bit hard to read.
++ for reminding me how horridble I am at even simple math without scratch paper, and for use strict :)
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