Any negative number should be zero

[hobbes1069]

Looks like you got it sorted. My random idea was to square it since the square of a negative number will be positive

[dceejay]

If you also know the maximum (or can guess one) - you can always just use a range node set to limit the range to the target range eg

\

That way anything outside will be clamped to the min (and max) values...

[9toejack]

@dceejay that will work for the psi for my fermenters, but not for inside functions when also using the psi data to calculate the volume of the boil kettle.
I did screen shot that on cell phone and added it to my project folder for further reference. Cheers