It would be great to have an input box, in which a user can enter something, which would then be referenced by a formula or something similar. Ideally there would be a way to enforce some sort of validation on the input, i.e. only accept integers, possibly even have regex as an option for validation.
At the moment I am using a select list so that a user can select, or even enter in the desired input. It would be easier to just have an input box.