Numberfield with no value?

[Insanity]

I've been developing a custom ruleset, and I came across an unique problem. In this game, weapons have range increments in which they have different accuracies. It is not simple as in D&D, -2 to hit for every range increment. It varies from weapon type and weapon. What I've done is set up an line of numberfields, one for every range inc., which is great, except for weapons in which they are not effective in a certain inc, the value has also been - (nothing, no value). I cannot show this using numberfields, their values range from i.e. -100 to 100, including 0. I need to include -100 to 0, no value, 0 to 100 and such. I've looked at windowreferencefield, but wasn't sure if this would do the job or not.

[Tokuriku]

If you have to use 0 and "no value", you obviously cannot put 0 as a hideon.
I have seen that you can imput -0 in FG if that helps... (taking -0 for no value).

[Insanity]

No good, if you enter -0 as a value, as soon as you click on something else, it becomes 0.