Variables integer or floating point?


I regular (every 15 mins) copy the value of the variable ‘temperature’ to a local variable ‘last temperature
Now when I use the value of these two variables in a comparison; whether they are above or below zero; then it seems the comparison sometimes fails.
My theory is that in the comparison the value of the variables are truncated to an integer and thus sometimes are exactly zero instead of for instance +0.02 or -0.02
Could this theory be true?
The problem is in that case that I can’t compare a variable to larger than or equal to zero. The ‘equal to’ option does not exist!

Regards Frank