public void addNeededVariables(final Set<String> neededVars) {
        if (formula != null) {
            neededVars.addAll(formula.getNeededVariables());
        } else {
            FormulaUtils.addNeededVariables(neededVars, getFormulaText());
        }
    }
Allows live-editing of a formula, optionally associated with a Variable List
main/src/main/java/cgeo/geocaching/ui/FormulaEditText.java