The outcome of the calculation is a rainfall depth, so in mm/h. That's always positive, and -9 isn't .
If $raintime is 0, the outcome should be 3.9E-4 mm/h (so almost nothing...)
$raintime is a value between 000 and 255 i think... But i think the problem is that its still a string, not a number.
I tried to convert the raintime to a number using:
but that didn't work.
I hope you guys can help me. Thanks for the effort so far!